HIGHWAY DESIGN MANUAL
Chapter 11 Signs, Signals, and Delineation
Revision 53
February 1, 2008
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SIGNS, SIGNALS, AND DELINEATION
Contents Page
11.1 INTRODUCTION......
11.1.1 General Design Considerations...... 11.1.2 Use of the Manual of Uniform Traffic Control Devices ......
11.2 SIGNS ......
11.2.1 General Sign Issues...... 11.2.2 Regulatory Signs ...... 11.2.3 Warning Signs...... 11.2.4 New York State Scenic Byways Sign Manual ...... 11-100 11.2.5 Decorative Community Gateway Signing and/or Landscaping on New York State Highway Right of Way ...... 11-100
11.3 TRAFFIC SIGNALS...... 11-101
11.3.1 Types Of Signals...... 11-101 11.3.2 Vehicle Detection Systems ...... 11-121 11.3.3 Signal Operation Design ...... 11-135 11.3.4 Plans and Specifications ...... 11-179 11.3.5 Terminology ...... 11-186 11.3.6 References...... 11-198
11.4 PAVEMENT MARKINGS ...... 11.4.1 Purposes of Markings ...... 11.4.2 Definitions and Terminology ...... 11.4.3 Types of Pavement Marking Systems...... 11.4.4 Roadway Surface Preparation...... 11.4.5 Policies on Permanent Pavement Markings ...... 11.4.6 Construction Zone Pavement Markings......
11.5 DELINEATORS AND OTHER DEVICES 11.5.1 Delineators...... 11.5.2 (SAFESTRIP) Rumble Strips...... 11.5.3 Object Markers ......
NOTE: Material in italics is in development and will be issued at a later date.
2/1/08 SIGNS, SIGNALS, AND DELINEATION
LIST OF TABLES
Number Title Page
Table 11-1 Definitions of Lane Control Signal Displays...... 11-102 Table 11-2 Four-Hour Volume Warrant ...... 11-105 Table 11-3 Reduced Four-Hour Volume Warrant...... 11-106 Table 11-4 Peak-Hour Volume Warrant ...... 11-107 Table 11-5 Reduced Peak-Hour Volume Warrant...... 11-108 Table 11-6 Nonintersection Pedestrian Signal Operation...... 11-112 Table 11-7 One-Lane Signal Control Operation ...... 11-113 Table 11-8 Emergency Vehicle Operation at Stop-and-Go Signals ...... 11-118 Table 11-9 Emergency Vehicle Operation at Normally Flashing Signal...... 11-118 Table 11-10 Emergency Vehicle Operation at Nonintersection Location ...... 11-120 Table 11-11 Comparison and Application of Several Vehicle Detector Types ...... 11-124 Table 11-12 Loop Inductances ...... 11-129 Table 11-13 Longitudinal Location of Vehicle Detectors ...... 11-134 Table 11-14 Two-Phase Traffic Signal Operation...... 11-139 Table 11-15 Advantages of Lead and Lag Left-Turn Operation ...... 11-141 Table 11-16 Disadvantages of Lead and Lag Left-Turn Operation ...... 11-142 Table 11-17 Signalized Intersection with Protected/Permitted Left-Turn Phasing...... 11-144 Table 11-18 Signalized Intersection with Protected Left-Turn Phasing...... 11-146 Table 11-19 Operation for Offset Intersections with Three-Phase Operation...... 11-148 Table 11-20 2-Phase Operation with Double Clearances ...... 11-150 Table 11-21 6-Phase Sequential Mode of Operation ...... 11-152 Table 11-22 Current Monitoring Design Chart...... 11-167 Table 11-23 Current Monitoring Design Worksheet ...... 11-170
3/15/02 SIGNS, SIGNALS, AND DELINEATION
LIST OF FIGURES
Number Title Page
Figure 11-1 Emergency Vehicle Operation at an Intersection ...... 11-119 Figure 11-2 Emergency Vehicle Operation at Nonintersection Location ...... 11-120 Figure 11-3 High Sensitivity Head ...... 11-126 Figure 11-4 Quadrupole Layout...... 11-127 Figure 11-5 Phase Sequencing Relationships...... 11-137 Figure 11-6 Signalized Intersection with Protected/Permitted Left Turn Phasing...... 11-143 Figure 11-7 Signalized Intersection with Protected Left Turn Phasing ...... 11-145 Figure 11-8a Offset Intersection with Three Phase Operation...... 11-147 Figure 11-8b Offset Intersection with Two Phases and Double Clearance ...... 11-149 Figure 11-9 Intersection Requiring Six Phase Sequential Mode of Operation...... 11-151 Figure 11-10 Detector Jumping/Switching...... 11-163 Figure 11-11 Table of Quantities ...... 11-179 Figure 11-12 Table Of Operations ...... 11-180 Figure 11-13 Table of Clearances ...... 11-181 Figure 11-14 Table of Switch Packs ...... 11-182 Figure 11-15 Table of Input Wiring ...... 11-183 Figure 11-16 Table of Magnetic Detectors ...... 11-183 Figure 11-17 Table of Magnetometer Detectors...... 11-184 Figure 11-18 Table of Microwave Detectors...... 11-184 Figure 11-19 Table of Inductance Loop Design...... 11-185
3/15/02 11-100 SIGNS, SIGNALS, AND DELINEATION
11.2 SIGNS
11.2.1 General Sign Issues
Guidance to be developed at a later date.
11.2.2 Regulatory Signs
Guidance to be developed at a later date.
11.2.3 Warning Signs
Guidance to be developed at a later date.
11.2.4 New York State Scenic Byways Sign Manual
The New York State Scenic Byways Sign Manual provides New York State Department of Transportation staff, New York State Scenic Byways Management organizations, municipalities and others that are involved with the New York State Scenic Byways Program with information about scenic byway signs for the designated Scenic Byways of New York State. The manual establishes a brand identity for New York State’s Scenic Byways and provides the public with clear and consistent scenic byways signage throughout the state. Information about the policies and standards governing scenic byways signs, the sign planning process, the types of signs and guidance about obtaining, designing, specifying, and manufacturing is included.
The Manual is provided in Appendix 11A.
11.2.5 Decorative Community Gateway Signing and/or Landscaping on New York State Highway Right of Way
Refer to Appendix 11B for guidance regarding decorative community gateway signing and/or landscaping on New York State Highway right of way.
2/1/08 SIGNS, SIGNALS, AND DELINEATION 11-101
11.3 TRAFFIC SIGNALS
The uses of traffic signals and flashing beacons include assigning right of way at intersections, providing emphasis to a hazardous location, controlling some types of railroad-highway grade crossings, controlling travel lane use, and supplementing certain signs. The traffic control devices included in this section are traffic control signals, pedestrian signals, flashing signals, flashing beacons, special-purpose traffic signals, and devices used at railroad-highway grade crossings.
A traffic control signal can operate to the advantage or disadvantage of the vehicles and pedestrians being controlled. Analysis of traffic operations and other factors at a large number of signalized and unsignalized intersections, coupled with the judgment of experienced traffic engineers, has provided a series of warrants that define the minimum conditions under which signals may be justified. Consequently, the selection and use of this control device should be preceded by a thorough traffic engineering study of roadway and traffic conditions. On projects where traffic conditions may have changed since the existing traffic signals were installed, traffic engineering studies of the existing operation and phasing should be made to determine whether the type of installation and its operation meet the current requirements of traffic. As part of this study, the existing Traffic Signal Operation Specifications and Table of Operation should be reviewed. The Regional Traffic Engineering Group should have copies of these documents. No changes in traffic signal operation or installation of a new traffic signal should be included in a project without the concurrence of the Regional Traffic Engineer.
11.3.1 Types Of Signals
11.3.1.1 Lane-Use Signals
Lane-use signals are overhead signals which display indications to permit, or prohibit, the use of specific lanes of a roadway, or to indicate the impending prohibition of use. These installations are distinguished by signal placement over a certain lane, or lanes, of the roadway, and by their distinctive shapes and symbols. Supplementary signs are often used to explain their meaning and intent. The three basic applications of lane-use signals are:
• Reversible lane control operation. • Two-way left-turn lane operation. • Toll booth operation.
The meaning of lane control indications is prescribed in Section 1116 of the NYS Vehicle and Traffic Law and is shown in Table 11-1.
Section 275.3 of the New York State Manual Of Uniform Traffic Control Devices (NYS MUTCD, officially known as Title 17, Volume B of the Official Compilation of Codes, Rules and Regulations of the State of New York (NYCRR)) provides additional information on the design and use of lane- use signals.
3/15/02 §11.3.1.1 11-102 SIGNS, SIGNALS, AND DELINEATION
Table 11-1 Definitions of Lane Control Signal Displays Display Definition
Steady Downward Traffic facing a steady downward pointing green arrow signal may travel Green Arrow in any lane over which such signal is located.
Steady Red “X” Traffic facing a steady red “X” signal shall not enter or travel in any lane over which such signal is located.
Steady Yellow “X” Traffic facing a steady yellow “X” signal is thereby warned that the related green downward arrow indication is being terminated, that a red “X” indication will be exhibited immediately thereafter, and that traffic shall vacate, in a safe manner, the lane over which such signal is located.
Flashing Yellow Traffic facing a flashing yellow “X” signal may travel in any lane over “X” which such signal is shown preparatory to making a left turn, using proper caution.
11.3.1.2 Flashing Signals
A flashing signal is an intersectional traffic control device which displays flashing indications to approaching traffic on all approaches to an intersection to notify motorists of possible vehicular intersectional conflict. It displays flashing yellow indications facing traffic on the major street or highway and flashing red indications facing traffic on the minor highway. It shall never display flashing yellow indications facing all approaches. Flashing red indications may by displayed facing all approaches to an intersection. The meaning of flashing red and flashing yellow indications are prescribed in Section 1113 of the NYS Vehicle and Traffic Law.
Flashing signals may be used at intersections where emphasis of the stop requirement is needed, but conditions do not justify installing a traffic control signal. They may also be used at intersections where sight distance is severely restricted. The flashing red indications are particularly applicable where stop signs, stop ahead signs, or stop signs and stop ahead signs supplemented by stop sign beacons, have been ineffective in obtaining compliance with the stop requirement. The flashing yellow indications alert motorists to the location of an intersection and have been found effective in reducing certain types of accidents. The flashing yellow indications should not, however, be expected or used to reduce traffic speeds.
The only indications which may be operated as flashing indications are circular red and circular yellow. However, a continuously illuminated right green arrow indication may be displayed on an approach displaying flashing red where right turning traffic has no uncontrolled vehicular conflicts.
Stop signs shall be installed on the approach controlled by the flashing red indication, except when a green arrow is displayed on the approach. Stop signs shall not be used on approaches where green arrows are displayed.`
§11.3.1.2 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-103
When flashing red indications are displayed on all approaches to an intersection, stop signs shall be installed on all approaches. Each stop sign should be supplemented by an all-way sign (see NYS MUTCD).
A flashing red indication on a driveway approach to an intersection controlled by a traffic control signal is not considered a flashing signal.
Section 274 of the NYS MUTCD provides additional information concerning the design of flashing signals.
11.3.1.3 Traffic Control Signals
A traffic control signal is a device by which traffic is alternately directed to stop and permitted to proceed. Traffic control signal is defined in Section 154 of the NYS Vehicle and Traffic Law. Traffic control signals are sometimes referred to as 3-color signals or stop-and-go signals. The purpose of a traffic control signal is to assign right of way at an intersection.
The installation of a traffic control signal is an effective means of assigning right of way to traffic on at-grade intersections. However, many have the misconception that traffic control signal installations provide the solution to all traffic problems. This is not true. Traffic control signal installations typically reduce the overall capacity of the intersection, delay motorists, and often increase the frequency of rear-end accidents. Thus, prior to approval or denial of a traffic control signal installation, thorough traffic engineering studies, including traffic volume, approach speeds, physical conditions of the intersection approaches, and accident history of the intersection should be completed to determine if signalization is justified.
Traffic control signal installation decisions should be based upon engineering judgement and investigation of existing traffic conditions, existing physical characteristics, accident history, vehicular and pedestrian volumes, the 85th percentile speed of approaching vehicles, the anticipated traffic conditions for the location under study, and other factors. The warrants for the installation of a traffic control signal are defined in Section 271 of the NYS MUTCD. They are listed here for ease of reference:
Warrant No. Description 1 Minimum vehicular volume. 2 Interruption of continuous traffic. 3 Minimum pedestrian volume. 4 School crossing. 5 Progressive movement. 6 Accident experience. 7 System warrants. 8 Combination of warrants. 9 Four-Hour Volumes. 10 Peak-Hour Delay. 11 Peak-Hour Volume.
3/15/02 §11.3.1.3 11-104 SIGNS, SIGNALS, AND DELINEATION
The above warrants should be used as guidelines and do not represent requirements that traffic control signals be installed. Rather, they “outline minimum conditions under which a traffic control signal may be justified.” In the sections that follow, additional conditions that would make installations permissible are discussed. Traffic signals should generally not be installed unless one or more of the warrants are met. In exceptional cases, signals may be installed where no single warrant is met, but where at least 80% of the stated volume values in both Warrants 1 and 2 are met. Engineering judgment must enter into any decision on whether or not a traffic control signal should be installed. Trial of other remedial measures which cause less delay and inconvenience to traffic should precede installation of traffic control signals.
Traffic signal warrants are based upon, among other factors, the 8th highest hour volume on an average day. The vehicle volume warrants (Warrants 1 and 2) are met when, for each of any 8 hours (not necessarily consecutive) of an average day, the traffic volumes on both the artery and side road exceed certain designated levels (see NYS MUTCD Section 271). Although determining whether a volume warrant is met is relatively simple under existing conditions (i.e., conduct hourly traffic counts on a Tuesday, Wednesday, or Thursday (typically) and compare results to warrants), it is not as straightforward under projected (future) conditions. Even though a particular intersection on a project may not currently meet the volume warrants, it should be determined whether it will meet the warrants during the 5th year after construction (ETC+5). If so, consideration should be given to the installation of a traffic control signal as part of the project.
The traffic volume warrant for signalization (vehicle Warrants 1 and 2) may be reduced when the 85th percentile approach speed of traffic on the artery is greater than 40 mph, or the intersection under study lies within the built-up area of an isolated community having a population of less than 10,000. The minimum vehicular volumes at these locations are 70% of those for Warrants 1 or 2.
Another case where traffic volume warrants can be reduced is the combination warrant, Warrant 8. Under this warrant, signals occasionally (in exceptional cases) may be justified where no single warrant is met, but where Warrants 1 or 2 are satisfied to 80% or more of the stated values. Trial of other remedial measures which cause less delay and inconvenience to traffic should precede installation of traffic control signals under this warrant.
When the 85th percentile approach speed on the artery is greater than 40 mph, or the intersection under study lies within the built-up area of an isolated community having a population of less than 10,000, the traffic volumes required for Warrant 6, accident experience, include both a history of 5 signal-correctable accidents in 12 months and 56% of the values given for Warrants 1 or 2. (80% (required for Warrant 6) x 70% (for speed or isolation) = 56%).
For convenience we have shown Warrant 9, Four-Hour Volume and Warrant 11, Peak-Hour Volume in tabular form. The graphical representation shown in the NYS MUTCD may also be used.
A. Warrant 9 - Four-Hour Volume
The Four-Hour Volume Warrant is satisfied when, for any 4 hours of an average day, the volume on the major street (total of both approaches) and the corresponding volume on the
§11.3.1.3 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-105
Table 11-2 Four-Hour Volume Warrant
One-Lane Artery Two-Lane Artery One-Lane Artery Two-Lane Artery One-Lane Side Road One-Lane Side Road Two-Lane Side Road Two-Lane Side Road
Artery Side Road Artery Side Road Artery Side Road Artery Side Road
385 320 400 390 400 390 470 475
400 310 500 340 500 340 500 455
500 260 600 290 600 290 600 390
600 220 700 245 700 245 700 330
700 185 800 205 800 205 800 275
800 150 900 170 900 170 900 230
900 120 1000 140 1000 140 1000 195
1000 100 1100 120 1100 120 1100 160
1100 85 1200 100 1160 115 1200 135
1145 80 1300 85 >1160 115 1290 115
>1145 80 1350 80 ------>1290 115
------>1350 80 ------Notes: 1. Number of lanes is for the moving traffic on each approach excluding parking and auxiliary lanes. Auxiliary lanes may be counted as approach lanes if the traffic they carry represents a significant portion of the total volume on the approach. 2. Vehicles per hour on artery is total of both approaches including auxiliary lanes. 3. Vehicles per hour on side road is higher volume side road approach (one direction only, including auxiliary lanes)
higher volume minor street approach (one direction only) all exceed the volumes shown in Table 11-2 for the existing combination of approach lanes.
When the 85th percentile speed of the major street exceeds 40 mph, or when the intersection lies within a built-up area of an isolated community having a population less than 10,000, the four-hour volume requirement is satisfied when the volumes referred to above exceed the volumes in Table 11-3 for the existing combination of approach lanes.
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Table 11-3 Reduced Four-Hour Volume Warrant
One-Lane Artery Two-Lane Artery One-Lane Artery Two-Lane Artery One-Lane Side Road One-Lane Side Road Two-Lane Side Road Two-Lane Side Road
Artery Side Road Artery Side Road Artery Side Road Artery Side Road
270 220 280 275 280 275 340 330
300 205 300 265 300 265 400 290
400 160 400 210 400 210 500 225
500 125 500 165 500 165 600 175
600 95 600 125 600 125 700 135
700 70 700 100 700 100 800 105
750 60 800 80 800 80 890 80
>750 60 900 60 >800 80 >890 80
------>900 60 ------Notes: 1. Number of lanes is for the moving traffic on each approach excluding parking and auxiliary lanes. Auxiliary lanes may be counted as approach lanes if the traffic they carry represents a significant portion of the total volume on the approach. 2. Vehicles per hour on artery is total of both approaches including auxiliary lanes. 3. Vehicles per hour on side road is higher volume side road approach (one direction only, including auxiliary lanes)
B. Warrant 11 - Peak-Hour Volume
The peak-hour volume warrant is also intended for application when traffic conditions are such that for one hour of a day, minor street traffic suffers extreme traffic delay in entering or crossing the major street.
The peak-hour volume warrant is satisfied when the volume on the major street (total of both approaches) and the corresponding volume on the higher volume minor street approach (one direction only) for one hour (any four consecutive 15 minute periods) of an average day, exceed the volume in Table 11-4 for the existing combination of approach lanes.
When the 85th percentile speed of the major street exceeds 40 mph or when the intersection lies within a built-up area of an isolated community having a population less than 10,000, the peak- hour volume requirement is satisfied when the volumes referred to above exceed the volume in Table 11-5 for the existing combination of approach lanes.
§11.3.1.3 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-107
Table 11-4 Peak-Hour Volume Warrant
One-Lane Artery Two-Lane Artery One-Lane Artery Two-Lane Artery One-Lane Side Road One-Lane Side Road Two-Lane Side Road Two-Lane Side Road
Artery Side Road Artery Side Road Artery Side Road Artery Side Road
500 425 500 520 500 520 600 600
600 375 600 470 600 470 700 540
700 325 700 420 700 420 800 480
800 280 800 370 800 370 900 425
900 240 900 325 900 325 1000 375
1000 205 1000 285 1000 285 1100 325
1100 175 1100 250 1100 250 1200 285
1200 150 1200 220 1200 220 1300 250
1300 130 1300 190 1300 190 1400 220
1400 115 1400 165 1400 165 1500 190
1500 105 1500 140 1500 150 1600 165
1600 100 1600 120 >1500 150 1670 150
1700 100 1700 105 ------>1670 150
1800 100 1800 100 ------
>1800 100 >1800 100 ------Notes: 1. Number of lanes is for the moving traffic on each approach excluding parking and auxiliary lanes. Auxiliary lanes may be counted as approach lanes if the traffic they carry represents a significant portion of the total volume on the approach. 2. Vehicles per hour on artery is total of both approaches including auxiliary lanes. 3. Vehicles per hour on side road is higher volume side road approach (one direction only, including auxiliary lanes)
3/15/02 §11.3.1.3 11-108 SIGNS, SIGNALS, AND DELINEATION
Table 11-5 Reduced Peak-Hour Volume Warrant
One-Lane Artery Two-Lane Artery One-Lane Artery Two-Lane Artery One-Lane Side Road One-Lane Side Road Two-Lane Side Road Two-Lane Side Road
Artery Side Road Artery Side Road Artery Side Road Artery Side Road
300 325 355 360 355 360 400 445
400 270 400 335 400 335 500 370
500 220 500 285 500 285 600 310
600 180 600 240 600 240 700 260
700 145 700 200 700 200 800 215
800 115 800 165 800 165 900 175
900 95 900 135 900 135 1000 140
1000 80 1000 110 1000 110 1100 115
1100 75 1100 90 1045 100 1170 100
>1100 75 1210 75 >1045 100 >1170 100
------>1210 75 ------Notes: 1. Number of lanes is for the moving traffic on each approach excluding parking and auxiliary lanes. Auxiliary lanes may be counted as approach lanes if the traffic they carry represents a significant portion of the total volume on the approach. 2. Vehicles per hour on artery is total of both approaches including auxiliary lanes. 3. Vehicles per hour on side road is higher volume side road approach (one direction only, including auxiliary lanes)
C. Additional Considerations
The important items to remember regarding traffic signal installations are:
• They are an effective means to assign right of way. • Unwarranted installations could create hazards or inefficiencies such as delay, increased accidents, a reduction in capacity on the highway, or promote increased disobedience of traffic control signals. • A thorough traffic engineering study should be completed prior to installation.
D. Traffic Signal Removal
The same traffic engineering studies required to determine if a traffic signal is needed should also be completed for existing signalized intersections to determine if the signal is still needed or whether changes are needed to the signal operation. If these studies indicate that the traffic control signal is no longer justified, consideration should be given to removing it and replacing it with appropriate alternative traffic control devices. If the traffic signal was installed under the
§11.3.1.3 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-109
Accident Experience Warrant it should not be removed. The following steps should be used when considering the removal of a traffic control signal:
• If the signal was installed for reasons other than a standard warrant, determine if these reasons still prevail. • Determine the appropriate traffic control to be used after removal of the signal. • Notify local public officials and law enforcement agencies of the intent to remove the traffic signal. • Inform the public of the removal study, for example, by installing an information sign(s) with the legend TRAFFIC SIGNAL UNDER STUDY FOR REMOVAL at the signalized location in a position where it is visible to all road users. Press releases to local newspapers and radio and television stations should also be considered. • Remove any sight distance restrictions as necessary. If inadequate sight distance can not be increased to standard (See Chapter 5, Section 5.10.5.1 of this manual) the traffic signal should be retained. • Flash or cover the signal heads for a minimum of 90 days, and install the appropriate stop control or other traffic control devices. • Remove the signal heads if the engineering data collected during the removal study period confirms that the signal is no longer needed. The signal poles and cables should remain in place for a maximum of 1 year after removal of the signal heads for continued analysis.
The decision to install, remove or modify a traffic signal rests with the Regional Traffic Engineer. Accordingly, no changes in traffic signal operation or phasing, no new traffic signal installations, or traffic signal removal should be included in a project without the concurrence of the Regional Traffic Engineer.
Traffic control phasing and operation are discussed in Section 11.3.4 Signal Operation Design.
11.3.1.4 Pedestrian Signals
Pedestrian signal indications are traffic signal indications intended for the exclusive purposes of facilitating and controlling pedestrian traffic.
Pedestrians are required, by law, to obey vehicular signal indications, unless pedestrian indications are provided. The meanings of pedestrian signal indications are defined in Section 1112 of the NYS Vehicle and Traffic Law. When pedestrian indications are used:
• WALK - A steady WALK or walking person symbol indication shall be displayed only when vehicles are not permitted to move across the crosswalk by a green arrow indication. • DONT WALK - A flashing DONT WALK or upraised hand indication shall be displayed as the pedestrian change indication to indicate that a steady DONT WALK or upraised hand will follow, and that pedestrians should continue to cross, if started, but shall not start to cross in the crosswalk the indication controls. • DONT WALK - A steady DONT WALK or upraised hand shall be displayed to indicate that a pedestrian shall not start to cross in the crosswalk the indication controls.
3/15/02 §11.3.1.4 11-110 SIGNS, SIGNALS, AND DELINEATION
An audible message may be used to supplement pedestrian indications. The messages shall consist of steady or pulsating tones or coded sounds which commence at the beginning of, and cease at the end of, the pedestrian walk interval (NYS MUTCD Section 273.7). Where there are pedestrian indications for an adjacent crossing and the respective crossing intervals occur at different times, the tones or sounds associated with each crossing direction shall be different.
Verbal messages may also be used to supplement pedestrian indications. The message associated with the pedestrian walk interval (NYS MUTCD section 273.7) shall be “The (road identifier) crossing time begins now. Be alert for turning vehicles.” The message associated with the pedestrian change interval (NYS MUTCD section 273.7) shall be “Finish crossing (road identifier), but do not start to cross if you are at the side of the road.” Where there are pedestrian indications for an adjacent crossing and the crossing intervals occur at different times, the voices associated with each crossing direction should be different.
Pedestrian indications shall be provided in conjunction with traffic control signals under any of the following conditions:
• When a traffic control signal is installed under the minimum pedestrian volume (Warrant 3) or school crossing warrants (Warrant 4). (See Sections 271.5 and 271.6 of the NYS MUTCD.) • When an exclusive phase is provided for pedestrian movements in one or more directions, and all conflicting vehicular movements are stopped. • When, in the presence of sufficient pedestrian activity, vehicular indications are not visible to pedestrians, or are in a position which does not adequately serve pedestrians. • Established school crossings are at intersections signalized under any warrant.
Pedestrian indications may be provided under any of the following conditions:
• When the use of pedestrian intervals different from the associated vehicle intervals is necessary to minimize vehicle-pedestrian conflicts. • When it is necessary to assist pedestrians in making a safe crossing because no vehicular indication is displayed, such as on one-way roadways or opposite the stem of a T- intersection. • When multiphase indications, as with split phase timing, would tend to confuse pedestrians guided only by vehicular signal indications. • When pedestrians cross to an island during a particular phase and should not be permitted to cross the remainder of the roadway, or another roadway, during the same phase.
Where pedestrian phases are included, signal operations involve either shared vehicular and pedestrian phases, or an exclusive pedestrian phase. With a shared vehicular and pedestrian phase, vehicles permitted to cross the crosswalk are those turning on circular green indications and, unless prohibited, those right-turn-on-red movements from the crossed approach. With an exclusive pedestrian phase, red indications are displayed on all vehicular approaches and pedestrians may cross all approaches. Vehicles permitted to cross the crosswalk are those making right-turn-on-red movements from the parallel and crossed approaches, unless those movements are prohibited. Of the two, the shared vehicular and pedestrian phase is usually
§11.3.1.4 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-111 preferable from a traffic operations perspective. Exclusive pedestrian phases should be used only where conflicts between pedestrians and vehicles turning on a circular green indication cause unusual safety problems.
Pedestrian detectors, either push buttons or other types, should be conveniently located where they are accessible to persons with disabilities and near each end of all crosswalks. Where two crosswalks end at, or near, the same location, the detector should be positioned to clearly indicate the crosswalk to which each applies and/or appropriate signs should be installed on each push button post. Additional detectors may be required on islands or medians where a pedestrian may become stranded.
Pedestrian traffic actuated signals may be justified at nonintersection locations for the primary purpose of controlling and protecting pedestrians. Such signals may also be warranted at intersections where a positive pedestrian crossing interval is desirable. Typical examples of conditions under which these pedestrians signals are used are:
• Midblock locations in heavily developed commercial areas where heavy pedestrian crossing movements occur during a substantial portion of the day and where adjacent signalized intersections are more than 300 m apart. • At schools, entrances to private property, and other facilities which generate heavy pedestrian crossing movements. These signals on State highways are erected and operated at the expense of others under a permit from the Department. • Intersections where heavy pedestrian crossing movements occur, but where side road vehicular volumes may not be sufficient to justify signal control.
Pedestrian signals at these locations must meet traffic signal Warrant 3, Minimum Pedestrian Volume or Warrant 4, School Crossing, as shown in Section 271 of the NYS MUTCD.
These pedestrian-actuated signals normally operate with a continuous artery green interval, except that the right of way is transferred, upon demand, to pedestrians wishing to cross the artery. An appropriate clearance interval shall always follow each green interval.
The change from normal operation is accomplished by actuation of a push button. Each interval for the crossing period is fixed at a definite length. At the expiration of the allotted crossing interval, the signal automatically reverts to normal operation and remains there until the crossing period is again called by push button actuation. Assuming continued push button actuation after the expiration of a crossing period, the signal will remain on normal operation for a predetermined minimum time before the crossing period is again introduced. Section 273 of the NYS MUTCD contains additional information on pedestrian signals. Table 11-6 shows a typical signal operation at a nonintersection location.
3/15/02 §11.3.1.4 11-112 SIGNS, SIGNALS, AND DELINEATION
Table 11-6 Nonintersection Pedestrian Signal Operation Phase Artery Indications Pedestrian Indications
Normal Operation Green DONT WALK
1st Vehicle Clearance Yellow DONT WALK
2nd Vehicle Clearance Red DONT WALK Pedestrian Crossing Red WALK
1st Pedestrian Clearance Red Flashing DONT WALK
2nd Pedestrian Clearance Red DONT WALK
Flashing Operation Flashing Yellow Inoperative (dark)
11.3.1.5 One-Lane Road Signals
One-lane road signals assign the right of way, alternately, to movements in each direction, on sections of two-way highway where only one lane is available. Use of one-lane road signal control is justified when only one travel lane is available to traffic in both directions, and it is impractical to alternately assign use of the lane by other means.
Steady circular red, yellow, and green indications shall be used in one-lane road signals. Subdivision (f) of Section 1111 of the NYS Vehicle and Traffic Law defines their meanings and the required motorist actions at a nonintersection traffic control signal. With this type of signal control, 2 standard signal faces with three 300 mm lenses are required at each end of the controlled section of highway. Only circular indications shall be used. The signal heads may be suspended over the highway or installed as pedestal or bracket-mounted heads on the side of the roadway. Special care is necessary in locating the stop line at the approaches to these signals, to allow sufficient maneuvering room for vehicles traveling in both directions. The relationship between a stop line and its associated signal faces shall be as required by Section 272.11 of the NYS MUTCD.
A one-lane road signal should operate as a 2-phase full traffic-actuated signal to maximize the efficiency of an inherently inefficient traffic flow condition. An all red clearance interval should follow each phase in accordance with traffic requirements. The all red clearance interval is required to permit traffic which has entered on a green indication to clear the controlled section before opposing traffic is permitted to move. A sequence of intervals for a simple one-lane signal control operation is shown in Table 11-7.
When one-lane signal operation is used in a construction zone, it may be beneficial to use signal heads facing the single lane between the signal spans. These signal heads may facilitate the movement of workers and any traffic from driveways within the work area. In a construction zone, consideration should also be given to controlling traffic from public roadways near or between the
§11.3.1.5 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-113 signal spans. Each of these installations should be considered on a case-by-case basis and it is recommended that the designer consult with the Regional Traffic Engineering Group concerning the need for additional traffic control.
Use of the rest-in-red feature of the Models 170/179 controller software may improve the efficiency of traffic flow. When no detector actuations are recorded in either vehicular phase, the signal clears to the rest-in-red (red on all signal faces) phase, where it remains until the next actuation. At the next actuation, green indications are immediately displayed in the demand direction. The Model 179 red revert feature provides a minimum red time prior to returning to the phase just terminated. The advantage of the rest-in-red is that the clearance is timed before demand exists, allowing immediate response to demand in either of the phases. A disadvantage of rest-in-red is that drivers begin to anticipate a green indication that will not occur if another phase is actuated first.
One-lane road signals shall operate continuously as a stop-and-go traffic control signal, as long as one-lane operation is in effect. See Section 275 of the NYS MUTCD for additional information on the design and operation of one-lane road signals.
Table 11-7 One-Lane Signal Control Operation PHASE DIRECTION "A" DIRECTION "B" PHASE 2 Circular Green Circular Red
1st Clearance to Phase 4 Circular Yellow Circular Red
All Red Clearance to Phase 4 Circular Red Circular Red
PHASE 4 Circular Red Circular Green
1st Clearance to Phase 2 Circular Red Circular Yellow
All Red Clearance to Phase 2 Circular Red Circular Red NOTE: Phases 2 and 4 are the recommended Model 179 phases to use for this operation. However, any two nonconcurrent phases could be used.
11.3.1.6 Drawbridge Signals
Traffic signals installed at drawbridges and other movable bridges are a specific application of traffic control signals. Drawbridge signals notify approaching traffic that a stop condition is imminent, due to road closure. Drawbridge signals should be used at all movable bridges. Section 275.4 of the NYS MUTCD outlines the installation and operation of drawbridge signals.
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11.3.1.7 Speed Control Signals
Speed control signals may be used at intersections, or at nonintersection locations, to moderate approach speeds. Actuated speed control signals lose some effectiveness under high volume conditions because heavy traffic extends the green indications regardless of speed. However, some degree of speed control is obtained, since the first vehicle is monitored as it approaches the signal, and the effect is reflected in the speed of the remaining vehicles of the group.
A speed control signal may be warranted where excessive approach speeds result in an abnormal accident record. Prior to installation of a speed control signal, a comprehensive traffic engineering study should be made to determine if alternate means, such as advance warning devices, can be used to moderate the approach speeds. At locations such as intersections, sharp curves, bridges, etc., where reduced approach speeds are desired, appropriate advance warning signs supplemented with flashing beacons provide positive and emphatic advance warning. These assemblies may provide the desired effect without stopping traffic.
See Section 275.5 of the NYS MUTCD for additional information concerning the design and operation of speed control signals.
11.3.1.8 Ramp Metering Signals
Ramp metering signals are traffic control signals installed on freeway entrance ramps to limit the rate at which traffic may enter the main roadway. Their effects are to reduce congestion and delay for mainline traffic, and increase delay for entering traffic. See Chapter 24 of this manual for a detailed discussion of ramp metering.
11.3.1.9 Traffic Control At and Adjacent to Railroad-Highway Grade Crossings
The railroad-highway grade crossing is a unique environment. Two modes of transportation are involved, the railroad train and highway traffic. This section discusses the traffic control employed for the highway user.
The function of traffic control systems at railroad-highway grade crossings is to provide appropriate information and sufficient time to permit roadway users to make relatively uncomplicated decisions that will allow them to safely pass over the crossing.
The various signals, signs, and pavement markings used to convey traffic control messages to highway users are classified as either passive or active. Passive crossing devices provide static messages of warning, guidance, and in some instances, mandatory action. Active crossing devices are those which give notice of the approach or presence of a train. They are activated by a train passing over a detection circuit, or, in a few situations, by manual control, and occasionally involve the use of a flagger.
Passive railroad crossing control devices consist of regulatory, warning, and guide signs and supplemental pavement marking. The NYS MUTCD specifies the use of these various devices.
§11.3.1.9 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-115
When used by themselves, passive crossing devices provide the minimum level of warning and/or control. Their use is also necessary in conjunction with active crossing devices to provide increased levels of warning and/or control.
Active traffic control devices include flashing light signals and automatic gates, with bells sometimes used as an audible supplement. Automatic sidewalk gates are also used where there are sidewalks leading to the crossings. In addition, highway traffic signals at or near grade crossings are sometimes connected to track circuitry to preempt certain highway intersection signal indications upon the approach of trains. Also, train activated yellow flashing beacons are sometimes mounted on the advance warning signs to create an active advance warning sign.
Grade crossing elimination and ultimately grade crossing separation of the railroad and highway are also traffic control alternatives to be considered.
At-grade crossings controlled by gates, the activated gates may be circumvented by a vehicle which goes to the opposing traffic lane and around the gate or a pedestrian who goes under or around the gate. There are preventive measures that can be employed at crossings where this is a problem.
Four-quadrant gate systems or curbed medians separating opposing lanes may be installed to restrict vehicle transgressions.
Fencing may be used to enclose the right of way, restricting pedestrian access to the crossing. However, fencing is generally ineffective at most grade crossings. One alternative is to provide a pedestrian grade crossing and to erect a fence to channelize pedestrians to the crossing. Such a crossing can be controlled with a train-activated gate and appropriate signing.
Grade-separated pedestrian overpasses can be used at reasonable intervals. However, pedestrian use of such structures will depend on their accessibility and ease of use. Underground tunnels are discouraged because they tend to encourage and provide cover for acts of crime.
Driver and pedestrian education is an effective method of reducing the incidence of accidents.
No form of protection can be effective without some level of surveillance and enforcement.
To determine the appropriate traffic control at a railroad-highway grade crossing, the designer should confer with the Regional Traffic Engineer and the Regional Rail Coordinator.
11.3.1.10 Flashing Beacons and Stop Sign Beacons
A flashing beacon consists of two or more flashing yellow indications facing in one direction to emphasize a sign message or to warn approaching traffic of a potential hazard. Flashing beacons may be used at obstructions in, or immediately adjacent to, the roadway, or to supplement regulatory or warning signs. Flashing beacons shall not be used for delineation or channelization. A flashing beacon may be particularly valuable where there is need for a device sufficiently conspicuous to identify a potential hazard, or where it is desirable to emphasize a sign message
3/15/02 §11.3.1.10 11-116 SIGNS, SIGNALS, AND DELINEATION at certain times. A stop sign beacon may be used with a stop sign to emphasize the stop requirement. Flashing red indications are used with a stop sign beacon. These devices are used mainly at high accident locations. Section 274.3 of the NYS MUTCD contains information on the design and use of flashing beacons, and Section 274.4 addresses design and use of stop sign beacons. The installation details for flashing beacon sign assemblies is shown on standard sheet “PEDESTRIAN SIGNALS AND FLASHING BEACON INSTALLATION DETAILS”.
11.3.1.11 Emergency Vehicle Signals
An Emergency Vehicle Signal is a traffic control signal used to accommodate the movement of emergency vehicles, usually in one of the following ways:
• At an intersection of two or more highways, primarily to provide for emergency vehicle movements through the intersection on the emergency vehicle approaches. Emergency vehicle approach is defined as any total approach normally used by emergency vehicles. • At the intersection of an emergency vehicle driveway with the abutting roadway, primarily to provide for emergency movements on the exclusive emergency vehicle approach. Exclusive emergency vehicle approach is defined as any driveway which is intended primarily for use of emergency vehicles, such as a firehouse driveway. • At an existing, or otherwise justified traffic control signal, or system of traffic control signals, as an emergency vehicle phase added to provide for emergency vehicle movements.
As in the case of all traffic devices, an emergency vehicle signal should be provided only if there is a demonstrated need. Adhere to warrants and guidelines in the NYS MUTCD to prevent indiscriminate application with resultant motorist disregard for warranted installations.
Before considering the installation of an emergency vehicle signal, consider less sophisticated solutions to operational problems. It may be more practical and desirable to install an appropriate warning sign, or a warning sign and flashing beacon assembly, instead of an emergency vehicle signal. Emergency vehicle signals can cause operational problems, such as preventing emergency personnel from reaching the emergency station because of vehicles stopped for red indications. Violation of the red signal indication, with attendant accident potential, is only permitted to the operator of a emergency vehicle while responding to an emergency call. The factors to be considered in determining the need for an emergency vehicle signal include accident experience of emergency vehicles with other vehicular traffic, vehicular volumes and speeds, number and time of emergency vehicle movements, visibility of the emergency vehicle to approaching traffic, and sight distance along the highway where emergency vehicles enter the roadway or intersection. The warrants for emergency vehicle signals are listed in Section 276.2 of the NYS MUTCD.
Emergency entrance warning assemblies on the highway approaches to an emergency vehicle facility driveway may be a preferable and practical alternative to the installation of an emergency signal. Where sight distance is limited, or if all warrants for an emergency signal are met, the warning assemblies should be supplemented by flashing beacons. Each warning assembly consists of the appropriate intersection sign supplemented by a driveway entrance sign and, where appropriate, a flashing beacon. The flashing beacon, if included, shall be illuminated only during
§11.3.1.11 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-117 emergency periods.
Article 44, Section 1681(c) of the NYS Vehicle and Traffic Law prohibits the Department from paying for the installation and maintenance of traffic control signals or flashing signals at entrances to private property. Accordingly, most emergency vehicle signals are installed and maintained by permit issued to the emergency vehicle agency.
The operation of intersections containing an emergency vehicle approach is shown in Section 276.4(b) of the NYS MUTCD. Table 11-8 shows an example Table of Operation for an intersection which normally operates stop and go, and Table 11-9 shows the operation of intersections that normally operate in the flashing mode. Figure 11-1 is used with both tables.
Table 11-9 shows emergency operation at a traffic signal using a Model 179 controller. Preempt A is the Model 179 preempt that interrupts normal signal operation in as rapid a manner as safely possible to sequence directly to the preemption operation. Accordingly, it is generally used to accommodate those preemptions which require service as soon as possible. Preempt A provides the preemption operation by deleting signal phases that are not required. In the example, the operation on Street B requires the use of both phases 2 and 6 during normal operation. To provide green indication on faces 3 and 4 during the preemption operation, all phases except phase 6 would be deleted. At the termination of emergency vehicle operation and prior to return to normal operation, vehicle actuations will automatically be placed for all actuated phases. However, if a phase is operating with the detector memory off (see Section 11.3.2) then the actuation will be dropped, unless there is a vehicle in the detection zone. The signal phase that would follow the preemption phase during normal operation will follow the preemption phase provided that an actuation remains for that phase. The signal may be equipped with one or more telltale indicators that are illuminated when the signal displays the emergency vehicle indications (see NYS MUTCD Section 276.3). The telltale indication must be connected to the yellow output of switch pack 11.
At intersections containing an exclusive emergency vehicle approach, the emergency vehicle signal shall operate as shown in Section 276.4 of the NYS MUTCD. However, no indications are required facing the exclusive emergency vehicle approach. If the exclusive emergency vehicle approach is not controlled, the driver of an emergency vehicle shall have a view of a telltale indication or other means of determining when the signal is in the emergency vehicle phase. If indications are provided for the exclusive emergency vehicle approach, during normal operation the face or faces may display flashing red in lieu of a steady red indication. If the signal normally operates as a flashing signal, the ten-second artery green interval may be reduced, if necessary. Vehicle detection will be necessary if (1) the signal normally operates as a stop-and-go signal, and (2) a steady red indication is used facing the exclusive emergency vehicle approach, and (3) nonemergency traffic is permitted to use the exclusive emergency vehicle approach.
Preemption of signalized intersections by emergency vehicles is done through the use of radio or light-beam transmitters on the vehicles to receivers on the signalized approach. Push buttons at the emergency vehicle station or dispatcher activation of a predefined route timing may also be used. Any preemption detection equipment used must be interfaced with the Model 170/179 signal controller.
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Table 11-8 Emergency Vehicle Operation at Stop-and-Go Signals FACES
PHASE 1 and 2 3 and 4 5,6,7 and 8 A
2 + 6 Green Green Red DONT WALK
Clearance to 4 Yellow Yellow Red DONT WALK Clearance to preempt A Yellow Green Red DONT WALK
4 Red Red Green DONT WALK (3)
Clearance to 2 + 6 Red Red Yellow DONT WALK
Clearance to Preempt Red Red Yellow DONT WALK
Preempt A (Phase 6) Red Green Red DONT WALK
Clearance to 2 + 6 Red Green Red DONT WALK Notes: 1. At the termination of emergency vehicle operation and prior to return to normal operation, vehicle actuations will automatically be placed for all actuated phases. 2. The signal may be equipped with one or more telltale indicators which are illuminated when the signal displays the emergency vehicle indications (see NYS MUTCD Section 276.3). 3. This indication will be WALK followed by a flashing and steady DONT WALK pedestrian clearance interval if a pedestrian push button has been actuated.
Table 11-9 Emergency Vehicle Operation at Normally Flashing Signal FACES
PHASE 1 and 2 3 and 4 5,6,7 and 8
Normal Operation Flashing Red Flashing Red Flashing Yellow
Clearance to Artery Phase Red Red Yellow
Phase 2 (Artery) Red Red Green
Clearance to Preempt A Red Red Yellow
Preempt A Red Green Red
1st Clearance to Normal Operation Red Yellow Red 2nd Clearance to Normal Operation Red Red Red Notes: 1. Pedestrian Indications would not be used at this type of signal. 2. The artery phase should be at least 10 seconds.
§11.3.1.11 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-119
Figure 11-1 Emergency Vehicle Operation at an Intersection
The operational requirements for emergency vehicle signals at nonintersection locations are described in Section 276.5 of the NYS MUTCD. These signals are installed primarily to accommodate emergency vehicle movements at isolated locations where the exclusive emergency vehicle approach is the only side road approach to the signal.
These signals may normally operate as a stop-and-go signal displaying green indications on the highway approaches, or as a flashing signal displaying flashing yellow indications on the highway approaches. No indications are required facing the emergency vehicle approach. If an indication or indications are used facing toward the exclusive emergency vehicle approach, they may display steady red, flashing red, or be inoperative. Steady red indications may be used on the exclusive emergency vehicle approach only when neither highway approach is controlled by flashing yellow indications. If a steady red indication is used facing the exclusive emergency vehicle approach and nonemergency traffic is permitted to use the exclusive emergency vehicle approach, vehicle detection will be necessary. Figure 11-2 and Table 11-10 show an example operation at a nonintersectional location using a Model 179 controller.
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Figure 11-2 Emergency Vehicle Operation at Nonintersection Location
Table 11-10 Emergency Vehicle Operation at Nonintersection Location FACES
PHASE 1, 2, 3 and 4 5
Normal Operation (Phase 2) Green Flashing Red 1st clearance to preempt Yellow Red
2nd clearance to preempt Red Red
Preempt A Red Green
1st Clearance to Normal Operation Red Yellow
2nd Clearance to Normal Operation Red Red Notes: 1. Face 5 is not required or may operate as a steady red indication during normal operation. An additional traffic signal face will be required facing the exclusive emergency vehicle approach if face 5 operates as a steady red during normal operation. If face 5 operates as a steady red, and nonemergency traffic is permitted to use that approach, then vehicle detection is required. Face 5 may only operate as a steady red indication when the highway approaches are not controlled by flashing yellow indications. 2. This signal may normally operate as a flashing signal.
§11.3.1.11 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-121
11.3.2 Vehicle Detection Systems
The operational efficiency of any traffic-responsive system depends on its ability to sense the presence of traffic. Traffic sensing is accomplished by a device commonly referred as a detector. Traffic detectors may be used to measure presence, volume, speed, and occupancy. Traffic detectors are used at individual signalized intersections, in coordinated traffic-responsive signal systems, or for ramp and freeway operations. For example, at an actuated signalized intersection, decisions such as extending the green for a vehicle or assigning the right of way to it at the earliest opportunity are based upon detector inputs to the intersection controller. The controller will process the inputs and make a decision as to how the intersection will be phased and timed. Detection systems are made up of three components:
• A device (sensor) placed in/under or above/alongside the roadway to sense the passing or presence of traffic. • A detector amplifier module generally placed in the traffic signal controller cabinet. • A lead-in cable (a group of separately insulated wires wrapped together) to connect the sensor to a detector amplifier.
This section will discuss traffic inductive loop, magnetic, magnetometer, and microwave detectors. These detectors are the most widely used in New York State. There are several other types of detectors such as pressure, radar, sonic light emission photoelectric, infrared, and video camera that have been used in the past or are under development. For information on these types of detectors check with your Regional Traffic Engineering Group. Information on detector amplifier modules can be found in the latest New York State Transportation Management Specifications published by Traffic Engineering and Highway Safety. Information on lead-in cables is included in the NYS Standard Specifications.
11.3.2.1 Detector Modes of Operations
Before selecting the type of detector to be used, the engineer must consider the traffic variables to be measured. Detectors are designed to sense either the presence of a waiting vehicle or the passage of a through vehicle.
A. Pulse Mode
The passage or motion of a vehicle is sensed by detectors which operate in the pulse mode. Each vehicle crossing the detector transmits a single pulse to the controller, regardless of the time a vehicle spends in the detection area. Detectors operated in the pulse mode are often referred to as point detectors. With this mode, the memory feature on the traffic signal controller for the traffic phase associated with the detector should be placed in the memory on (locking) mode.
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B. Presence Mode
In presence mode, a continuous call is provided to the controller as long as a vehicle is within the detection area. Presence mode is used for detectors arranged to cover an area rather than a point. These detectors are generally used in left turn lanes or on low speed (40 km/h or less) approaches to an intersection. With this mode, the memory feature on the traffic signal controller for the traffic phase associated with the detector should be placed in the memory off (nonlocking) mode.
11.3.2.2 Detector Types
This section provides technical information for vehicle detectors used in modern day traffic signal control.
A. Magnetic Detector
Magnetic detectors operate on the basis of a change in the lines of flux from the earth's magnetic field. A coil of wire with a highly permeable core is placed below the surface of a roadway. When a vehicle comes near to or passes over the coil, the constant lines of flux passing through the coil are deflected by the vehicle, thus causing a voltage to be induced in the coil. A high-gain amplifier enables this voltage to operate a relay, which sends a message to the controller that a vehicle has been detected. A magnetic detector is a passive device which does not create a field around it. Accordingly, a vehicle must be in motion through the zone of influence to create a call to the controller. This type of detector is not suitable where vehicle presence detection is required or where speeds are below 8 km/h.
The magnetic detector is a bullet-shaped probe that is installed under the roadway inside a nonferrous conduit (see standard sheet “MAGNETIC VEHICLE DETECTOR INSTALLATION DETAILS”). These units are insensitive to the direction of the vehicle and will respond to vehicles in any direction over an area as large as 4.8 m in diameter. Unless properly installed, this large area of sensitivity invites false actuations that defeat the purpose of the detector. The probe is pushed into a 3 NPS, nonmetallic conduit from the roadside access hole at the curb to a point beyond the centerline of the road. The probe can be located without interrupting traffic. Normally, a magnetic detector can be used to detect from one to three lanes of traffic.
The advantages and disadvantages of magnetic detectors are shown in Table 11-12.
B. Magnetometer Detector
A magnetometer detector system consists of the probe, probe cable, lead-in cable, and magnetometer vehicle detector module (detector amplifier). The detector measures a change in the vertical component of the earth's magnetic field caused by the presence or passage of a vehicle over the magnetic probe installed in the pavement. The magnetometer probe is a small cylindrical device, installed in a vertical position in a drilled hole in the pavement, usually
§11.3.2.2 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-123
0.3m deep (see standard sheet “MAGNETIC VEHICLE DETECTOR INSTALLATION DETAILS”). A single magnetometer probe is not recommended for defining vehicle speed and occupancy in a surveillance application because of the inaccuracy of locating the exact position of the vehicle with the probe. Sensitivity is very important to the magnetometer detector system. As many as 12 probes can be connected in series to one channel of a detector unit. However, as the number of probes per channel is increased, the sensitivity at each probe is decreased. Magnetometers are very good for pulse mode operation (point detectors) since they are capable of detecting two vehicles as close as 0.3 m apart.
Magnetometer systems will operate properly where the vertical component of the earth's magnetic field is in the range of 0.2 oersted to 0.75 oersted. Nearly all candidate sites are within these limits. However, care should be taken in probe site selection to either avoid questionable locations such as those close to manholes, large pipes, near trolley lines and underground subways, within tunnels or iron structures, and on bridge decks, or verify by prior measurement that the specific sites will be satisfactory. Magnetometer detectors will function near horizontal steel such as reinforcing bars, but probes must be kept 0.9 m to 1.2 m away from vertical steel. A magnetic field analyzer is used for probe site verification. Each detector channel comes with a pair of double probes spaced 3.05 m apart at the end of 15 m of lead-in cable.
See Table 11-11 for the advantages and disadvantages of magnetometer detectors.
C. Inductive Loop Detector
An inductive loop detector system consists of an insulated loop wire placed in a shallow slot sawed in the pavement, a lead-in wire to a curbside pull box, a shielded lead-in cable from the curbside pull box to the controller cabinet, and a loop detector module (detector amplifier) in the controller cabinet. The loop detector module drives energy through the loop system at frequencies in a range of 25 kHz to 170 kHz creating an electromagnetic field in the vicinity. When a vehicle passes over or is stopped over the loop, it decreases the induction in the loop, which causes the detector electronics to send an impulse to the controller signifying it has detected a vehicle. A 0.02% change in inductance at the detector module will register as a vehicle actuation. Loop detectors may be used in both pulse and presence modes.
An inductance loop can be arranged to encompass an area of detection or to sense a point of detection. An area of detection requires an elongated induction loop which operates in the presence mode. A point of detection requires a short inductance loop which operates in the pulse mode. Regardless of a loop's application (pulse or presence mode) the geometric arrangement of each loop is similar. All loops should have a width of 1.8 m. The length of a short loop should be 1.8 m. Normally, presence loop lengths are limited to 30 m maximum and are typically 21 m. The elongated presence loop should be installed such that the end of the loop nearest the intersection is at the stop line or no more than 20% of the loop is beyond the stop line. Loops should be located at least 0.6 m away from metallic object(s), such as covers of manholes or valves.
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Table 11-11 Comparison and Application of Several Vehicle Detector Types
Detector Advantages Disadvantages Application Type
Microwave -Immune to electromagnetic -Relatively expensive if Microwave detectors can be interference. existing poles not used for both point and -Can be mounted side fire. available for use. presence detection. -Relatively easy to install. -May require FCC license Microwave detectors are -Capable of measuring all to operate. useful for roadways where traffic parameters (count, -Some units cannot the pavement is deteriorating presence, speed and measure presence. or on bridge decks. In the occupancy). side-fire position microwave detectors are useful for detection on driveways. Microwave detectors are also appropriate for detection at temporary signals.
Magnetic -Installed under roadway. -Nondirectional. Magnetic detectors may be -Relatively easy to install. -Cannot detect presence. used on high-speed -Low maintenance costs. -Cannot be installed on approaches where point -Easily replaced. bridge decks. detection is combined with -Difficult to set detection memory on (locking) on the zone. controller, and in areas with -Subject to false calls poor pavement conditions. where located near large power lines.
§11.3.2.2 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-125
Table 11-11 Comparison and Application of Several Vehicle Detector Types (continued)
Detector Type Advantages Disadvantages Application
Magnetometer -Works on road surfaces -Cannot be used near devices Magnetometer detectors where inductance loops which generate changing are used primarily to and magnetics cannot magnetic fields. provide vehicle counting be used (bad or brick -Requires closing of traffic and passage information pavements). lane for installation. at intersections where the -Excellent for pulse -May double-count some device senses vehicles mode operation (point vehicles due to magnetic within a small area (point detection). material distribution. detection). A large-area -Relatively easy to -Poorly defined detection detection application install. zone. requires a series of -Capable of count or -More expensive than probes, which is more presence detector. magnetic detector. costly than a loop -Not affected by power detector. Magnetometers lines in vicinity. may be used under bridge decks when damage to the reinforcing steel is a concern, or in roadways where the pavement is deteriorating and the linear feet of saw cut must be kept to a minimum.
Induction Loop -Detection area can be -Requires closing of travel The induction loop set by the size of the lanes for installation. detector is by far the loop. -Cost of installation may be most commonly used -Excellent for presence excessive. detector. Loop detectors detection. -Cannot be used in poor may be used for both -Capable of measuring pavement. point and presence all traffic parameters. -Cannot be used on bridge detection. -Under roadway location decks. and not subject to -Subject to damage by damage except in poor pavement movement (frost, pavement. etc.). -Relatively easy to install. -Relatively inexpensive to abandon loop and reuse amplifier at new location.
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C.1 Long Loops. The long loop (elongated inductance loop) is used to detect the presence of a vehicle. An approach where speeds are low (40 km/h or less) or where most of the traffic makes a right or left turn onto the cross street (regardless of approach speeds) should be considered for long loop installation. Long loops are particularly well suited for use in left turn lanes with separate traffic signal phases or in right turn lanes with a right green arrow displayed during a cross street left turn phase. Long loops are also useful in right turn lanes or through/right lanes when a large number of vehicles make right turns on red.
There are precautions that must be considered before using an elongated presence loop. Long loops tend to have inadequate sensitivity. Attempts to increase the sensitivity may result in false actuations from vehicles in adjacent lanes (splash over). Lack of sensitivity, especially at the center of the loop, may result in failure to detect a small vehicle or to hold the detection for an adequate length of time. Where there are a significant number of motorcycles on an approach where an elongated loop will be used, a high sensitivity head should be installed at the end nearest the stop line. The high sensitivity head is a 1.8 m by 1.8 m loop within the long loop. The loop wire is continuous as shown schematically in Figure 11-3 below. The standard power head can be improved by angling the transverse wire to form a parallelogram in the direction of traffic flow. Another way to provide the function of the power head would be to install a separate loop in a parallelogram configuration at the stop line.
Figure 11-3 High Sensitivity Head
Multiple small loops offer greater control of both sensitivity and inductance. In addition, they provide better detection of small vehicles, greater resistance to loop damage, and easier adjustment of the length of the detection area. Multiple loop systems also maintain actuated control if one loop fails. Improvement in detector electronics and innovative long loop configurations such as the quadrupole are the most recent answers to long loop sensitivity problems. The quadrupole loop configuration consists of 2 narrow loops laid side-by-side with a polarity of winding such that their fields cancel each other outside of the loop perimeter and are enhanced within its confines. The quadrupole loop design provides excellent immunity from crosstalk. The quadrupole configuration also minimizes adjacent lane actuations (splash over) and environmental noise. This arrangement is shown in Figure 11-4.
§11.3.2.2 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-127
Figure 11-4 Quadrupole Layout
Long loops are vulnerable to actuations by a vehicle turning from the cross street. Left turning vehicles tend to cut across the stop line when there is no traffic waiting on the approach. Proper location of the stop line (and therefore the loop) can help overcome this. Also, phases that have long loop presence detection are typically operated with the memory/recall on the controller in the memory-off mode. This helps to ease the problem of false actuations. (The "memory/recall" in a signal controller is a feature whereby the signal remembers that a vehicle has crossed a detector while the light is either yellow or red.) Also, a detector delay could be programmed for the long loop. With this feature, a vehicle must be over the loop for the programmed time before the controller will accept a call from the detector. Long loops do not provide dilemma-zone protection.
C.2 Short Loops (Point Detection). A short inductance loop is normally installed to detect motion of a vehicle and is operated in pulse mode. It may also be used as a calling detector when there are driveway entrances to the highway between the primary detector and the stop line where vehicles may enter the approach from the driveway without placing a call for the traffic signal phase on this approach (since the vehicles do not cross the detector). When the signal is red and there are no other vehicles approaching to actuate the detector, these vehicles can be trapped at the stop line. A detector installed near the stop line (calling detector) prevents this. This detector will only place a call when the signal is red and a call does not already exist for the associated signal phase. The calling detector will only place one call until the affected phase times its green interval.
C.3 Combined Point and Presence Detection. By installing a point and a long loop detector on each high speed approach to the intersection, the advantages of both are provided. For this operation, the memory/recall in the signal controller for the signal phase the detector is associated with must be in the memory/off mode. The required time needed to hold the vehicle actuation while a vehicle passes from the point loop to the long loop would be provided by the detector extension feature of the Model 179 controller. The major disadvantage of this type of operation would be the increased installation and maintenance cost for the additional detectors.
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See Table 11-11 for the advantages and disadvantages of induction loop detectors.
C.4 Inductive Loop Design
C.4.a General. One of the advantages of the inductive loop detector is the wide range of permissible loop geometries. The size and number of turns of the loop wire or combination of loops, together with the length of lead-in wire, must produce an inductance within a range that is compatible with the design of the detector amplifier and the system requirements. If the inductance falls outside of the required range, the detector will not operate properly. NYSDOT Models 222 and 224 loop detector modules are designed to operate within an inductance range of from 50 microhenries (µh) to 2000 µh. Loop layout and size are engineering considerations and should be determined by the detection requirements of the intersection approach and the capabilities of available equipment.
C.4.b Loop Configuration. The magnetic field emanating from the loop wire extends from 0.9 m to 1.2 m on each side of the loop wire. The width of the loop should be 1.8 m to ensure that there are no dead spots and that an adequate detection area is provided. To be detected, a vehicle must cross over, or occupy, at least 15% of the loop perimeter being accommodated by a single detector channel. The length of the loop and the number of turns is governed by the inductance of the loop system and the tuning range of the detector amplifier, as well as the detection requirements of the approach.
Loops are conventionally installed in a rectangular configuration. A quadrupole configuration, shown in Figure 11-4, eliminates adjacent lane detection, a problem which plagues high- sensitivity rectangular loops needed to detect motorcycles and bicycles. Quadrupole loops are installed so that the center wires have currents flowing in the same direction. Their fields reinforce each other and improve the capability of detecting small vehicles. The center wires counteract the fields of the outer wires which have their currents flowing in the opposite direction from the center wires. The influence of the outer fields is diminished, reducing the possibility of splash over. The 1-2-1 configuration shown in Figure 11-4 is intended for detection of automobiles, trucks, and large motorcycles. A 2-4-2 configuration is recommended for detection of bicycles and small motorcycles. Lateral placement is very important. Many times, the loop will be placed in the middle of the lane and a motorcycle will not be detected because of the path that the motorcyclist travels. Since motorcyclists wanting to turn left usually stop on the left side of the lane, they may easily be outside the quadrupole field. In a lane where vehicles require detection to turn left, the left edge of the quadrupole loop should be located at the stop line no farther than 600 mm from the centerline.
C.4.c Inductance
A prime design consideration is the verification that the total inductance of the loop and lead-in system connected to one detector channel will operate within the tuning range of available loop detector amplifiers. NYSDOT Model 222 and 224 loop vehicle detector modules are designed
§11.3.2.2 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-129
to operate correctly when connected to an inductance of from 50 µh to 2000 µh.
Total system inductance is equal to the inductance of the loop added to the inductance of the lead-in cable from the loop to the pullbox and to the detector input terminals inside the controller cabinet. Loop inductance may be obtained from Table 11-12. Inductance of the lead-in cable is added to the loop inductance at the rate of 20 µh per 30 m of cable.
Table 11-12 Loop Inductances CALCULATED LOOP INDUCTANCE (microhenries (µh)) Loop size (meters) 1 Turn 2 Turns 3 Turns 4 Turns
1.8 x 1.8 12 36 72 120
1.8 x 3.0 16 48 96 160
1.8 x 6.0 26 78 156 260
1.8 x 9.0 36 108 216 360
1.8 x 12.0 46 138 276 460
1.8 x 15.0 56 168 336 560
1.8 x 18.0 66 198 396 660 1.8 x 21.0 76 228 456 760
1.8 x 24.0 86 258 516 860
1.8 x 27.0 96 288 576 960
1.8 x 30.0 106 318 636 1060
Combinations of loops may be connected to the same detector unit in either series or parallel in order to keep the total inductance within the required 50 µh to 2000 µh range.
• Loops connected in series have an inductance L= L1+L2+L3+... Li. • Loops connected in parallel have an inductance L= 1/((1/L1)+(1/L2)+ ... (1/Li). • Two loops connected in parallel have a total inductance of (L1 x L2)/(L1+L2). • Only loops of the same size, shape, and inductance should be connected to the same detector channel.
When designing a loop and lead-in system, the total inductance should be kept between 60 µh and 1600 µh. This provides for a 20% safety factor with equipment currently in use. Avoid more than 225 m of lead-in cable per channel. If more than 300 m of lead-in is required, install a detector cabinet and detector amplifier between the detector and the controller cabinet. The following sample calculations illustrate the procedure for verifying that the inductance of a loop and lead-in system are within the allowable inductance range.
3/15/02 §11.3.2.2 11-130 SIGNS, SIGNALS, AND DELINEATION
SAMPLE CALCULATIONS FOR LOOP SYSTEM INDUCTANCE
ALL LOOPS IN ALL LOOPS IN PARALLEL COMBINATION SERIES- SERIES PARALLEL
• Two 1.8 m x 3.0 m • Three 1.8 m x 1.8 m • Two 1.8 m x 1.8 m 3-turn loops 3-turn loops 3-turn loops in parallel, • 152 m lead-in • 122 m lead-in connected in series to a 1.8 m x 1.8 m, 3-turn loop • 91 m lead-in
STEP 1 Obtain individual loop inductance from Table 11-11
L1 = L2 = 96 µh L1 = L2 = L3 =72 µh L1 = L2 = L3 = 72 µh
STEP 2 Calculate inductance of parallel loops (Lp)
Lp = 0 L1,2 = (L1x L2)/(L1+L2) = Lp = (L1 x L2)/(L1 + L2) (72 x 72)/(72 + 72) = 36µh Lp = (72 X 72)/(72 + 72) Lp = (L1,2 x L3)/(L1,2+L3) Lp = 36 µh Lp = (36 x 72)/(36+72) = 24
STEP 3 Calculate inductance of series loops (Ls)
Ls = L1 + L2 Ls = 0 Ls = L3 = 72 µh Ls = 96 + 96 = 192 µH STEP 4 Calculate loop system inductance (Ll = Ls + Lp)
Ll = 192 + 0 = 192 µh Ll = 0 + 24 = 24µh Ll = 72 + 36 = 108 µh
STEP 5 Calculate lead-in inductance values L'
L' = 152 x (20/30) = L' = 122 x (20/30) = 81 µh L' = 91 x (20/30) = 61 µh 101 µh
STEP 6 Calculate total loop system inductance (Lt = Ll + L')
Lt = 192 + 101 = 293 Lt = 24 + 81 =105 µh Lt = 108 + 61 = 169 µh µh
All three loop and lead-in systems are within the allowable induction range of 60 µh to 1600 µh.
C.4.d Sensitivity. A detector’s sensitivity is defined as the smallest change in total inductance of the loop and lead-in system which will cause the detector to actuate.
Detectors are actuated by a percent change in the total inductance. Detectors operating on a
§11.3.2.2 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-131
percent change basis are susceptible to decreased sensitivity due to large inductance values of long lead-in lengths. If the lead-in inductance is doubled, the change in inductance required to reach the percent change needed to actuate the detector also doubles. For this reason, the inductance of the loop should be as large as possible in relation to the inductance of the lead-in cable. Multiple loop design, unfortunately, can reduce the percent change in inductance that the detector can receive from any given loop in the combination. If a long lead-in and multiple loops are used together, care should be taken to make sure the percent change in inductance caused by a vehicle in the loop does not drop below the detector's sensitivity level.
Digital detectors measure frequency counts and operate on an absolute change basis instead of percent change. This makes digital detectors relatively immune to a decrease in sensitivity due to a long lead-in. The total inductance must still be within the tuning range of the detector.
The addition of pavement thickness over a loop causes a loss in sensitivity. A loss of 20 to 30 percent can be expected from typical overlays of 75 mm to 125 mm of thickness.
The NYS Models 222 and 224 loop vehicle detector modules are both digital detectors.
C.4.e Design to Minimize Crosstalk and Environmental Noise. When more than one channel of a loop detector module is used at the same general location, crosstalk may be a problem. Crosstalk is interference resulting from the overlapping electrical fields of loops located near each other and operating at or near the same frequency. Some detector units are designed to minimize crosstalk in various ways. The following design steps should be taken to minimize crosstalk.
1. Twisted pairs must be used for all cabinet lead-in and pullbox wiring. 2. Loops within 3 m of each other must be connected to the same detection channel or to different channels of the same detector unit. 3. Shielded lead-in must be used to eliminate coupling between loops. 4. Loop input leads should never be harnessed with other wires carrying significant transient signals, loop input to other detectors, or high-level AC signals in the 10 kHz to 100 kHz range. 5. If electrical noise is likely, a noise-canceling loop configuration, such as a Quadrupole, should be considered.
Details for the installation of inductive loop detectors can be found in Traffic Engineering and Highway Safety Division's Signal Installation Manual, the Standard Specifications, and on Standard Sheet “INDUCTANCE LOOP VEHICLE DETECTOR INSTALLATION DETAILS”.
D. Microwave Detectors
Microwave detectors transmit microwave energy toward the roadway from the detector’s antenna. The presence of a vehicle causes a reflection that is returned to the antenna. Many microwave detectors sense the frequency change of the reflected energy (Doppler frequency) and obtain vehicle speed from the signal. Other detectors use other properties of the reflected
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signal. Detectors that only use the Doppler frequency can sense only speed and passage, not presence.
Microwave detectors should be mounted on a stable pole which does not flex more than 5° and is situated close to the road or intersection. The outputs of the detector should be easily connected to the traffic signal controller. All detection zones must be aligned along a straight line from the pole. If this cannot be achieved, sometimes an extension arm from the pole may provide the solution. Avoid trees and other moving objects between the microwave detector and the required detection zones.
The mounting height of the detector should be sufficient so that vehicles are not masked by fixed obstacles or other vehicles. The height should be low enough so that all detection zones will be contained within a 50° elevation angle. In most cases a height of 5 m is preferred.
See Table 11-11 for the advantages and disadvantages of microwave detectors.
11.3.2.3 Detector Selection Criteria
The selection of the type of detector is determined primarily by suitability for the intended purpose. The decision whether a particular detector is appropriate for a certain purpose depends on its operating characteristics, its adaptability to the particular application, and the location specific details of the installation requirements.
A. Operating Characteristics
Section 11.3.2.2 described the operating characteristics of the four most frequently used detectors. Each is inherently unsuitable for certain applications because of inappropriate operating theory. For example, magnetic detectors can not be used for presence detection, as the vehicle must be in motion to produce a call. Magnetometers will function in the vicinity of horizontal steel such as reinforcing bars, but probes must be kept 0.9 m to 1.2 m away from vertical steel. Steel mesh beneath a loop detector has the effect of compressing the electrical flux field and reducing the sensitivity. A steel mesh 50 mm under a loop buried in concrete can halve the sensitivity of the same loop buried in asphalt. Since microwave detectors do not need to be in or under the approach to be detected, they are useful for detecting traffic on driveways.
§11.3.2.3 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-133
B. Site Specific Needs
The consideration of detection needs further narrows the range of detectors in some instances. For example both the loop and the magnetometer detector are suitable in theory for presence detection on a left-turn lane at a signalized intersection. Both are capable of doing the job. The loop, however, is significantly less expensive for this application. Another example would be an intersection approach where only rudimentary traffic responsiveness is adequate. A point detector of any of the four types would meet detection needs, but a magnetic detector might be chosen for its durability and low cost.
Another consideration would be eliminating a saw cut by replacing it with a drilled hole (magnetometer). A magnetic or microwave detector might be used at locations with deteriorated pavement.
The designer should discuss the type of detector to be used on any project with the Regional Traffic Engineering Group.
C. Installation
In areas of high traffic volumes it may be desirable to select a detector that can be installed without disrupting traffic or breaking pavement. If a suitable pole is already in place consideration might be given to a microwave detector.
11.3.2.4 Detector Longitudinal Location
The recommended longitudinal location of point vehicle detectors at a signalized intersection is shown in Table 11-13. These locations are based on the Traffic Engineering and Highway Safety Division’s December 1982 report titled Detector Location.
3/15/02 §11.3.2.4 11-134 SIGNS, SIGNALS, AND DELINEATION Design Speed (km/h) 02 20.54 19.56 33.7 18.68 31.8 50.1 17.8 30.2 47.2 17.0 69.7 28.8 44.6 65.4 27.5 92.4 42.4 61.7 86.6 40.4 118.2 58.5 81.6 110.7 147.4 55.7 77.2 104.2 137.8 179.6 73.4 98.5 129.5 167.8 215.0 93.5 157.6 122.3 200.7 233.9 116.0 188.3 148.7 218.2 140.9 204.7 177.6 168.2 193.0 182.7 -8-6 27.3-4 25.1-2 45.8 23.3 41.8 69.0 21.8 38.6 62.8 96.9 36.0 57.7 87.9 129.4 53.6 80.6 117.2 166.7 74.7 107.3 150.7 208.6 99.2 137.8 188.4 255.2 172.1 127.2 230.3 306.5 210.1 158.6 276.3 333.9 252.0 193.5 300.9 274.3 231.9 252.3 10 16.4 26.4 38.7 53.2 70.0 89.1 110.4 134.0 159.8 173.6 -10 30.2 50.9 76.9 108.3 144.9 186.9 234.2 286.9 344.8 375.8 % Grade 30 40 50 60 70 80 90 100 110 115 Table 11-13 Longitudinal Location of Vehicle Detectors (meters from stop line)
§11.3.2.4 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-135
11.3.3 Signal Operation Design
After it has been found that a signal is needed at a particular location, the designer must determine the most appropriate method of control. The full benefit of a traffic control signal is realized only when it is operated as near as possible to actual traffic requirements. Operational and safety problems can follow unnecessary, arbitrary, or inappropriate operation. The operational decisions to be made are shown below.
• Signal phasing. • Emergency vehicle phasing. • Pedestrian phasing. • Type of signal operation (pretimed, semi-traffic-actuated or full-traffic-actuated). • Detection alternatives. • Model 179 time clock and programmable features. • Assignment of switch packs. • Interconnection considerations.
11.3.3.1 Signal Phasing
A signal phase is defined as that part of the signal cycle allocated to a group traffic movement or a combination of nonconflicting group traffic movements receiving the right of way simultaneously. A traffic movement may be a vehicular movement alone, a pedestrian movement alone, or combinations of vehicular and pedestrian movements.
NYSDOT Models 170/179 traffic signal controllers use the National Electrical Manufacturers Association (NEMA) nomenclature for defining traffic signal phases. The Models 170/179 provide both an 8-phase dual ring sequencing mode and a 6-phase sequential mode.
In the 8-phase dual ring mode, the phases are grouped into two rings of 4 phases each, and two combinations of 4 phases each (see Figure 11-5). The ring and combination grouping concept will determine the order in which the phases are served, as well as which phases can be served concurrently.
Figure 11-5 is from Traffic Engineering and Highway Safety’s Traffic Actuated Processing System Operator’s Manual and shows the two combination concept. Phases 1, 2, 5, and 6 are grouped into what is called combination 1. Phases 3, 4, 7, and 8 are grouped into combination 2.
Figure 11-5 also shows the two ring concept. Phases 1, 2, 3, and 4 are grouped into what is called Ring "A". Phases 5, 6, 7, and 8 are grouped into Ring "B".
In the dual ring mode, phases are timed in a preferred sequence, while allowing concurrent timing of compatible phases in either ring within the same combination. When the controller receives calls to serve the various phases in the signal operation, it will always serve the phases in accordance with three criteria that apply to the rings and combinations. They are as follows.
• No more than 2 phases may be active at the same time.
3/15/02 §11.3.3.1 11-136 SIGNS, SIGNALS, AND DELINEATION
• Only 1 phase in each ring may be active at the same time. • Only phases in the same combination but different rings may be active at the same time.
Figure 11-5 shows the potential sequence of operation by the controller (concurrent phasing), assuming calls for all phases. It starts the sequence by allowing the timing of Phases 1 and 5. From that point, there are 3 possible paths to follow, depending upon traffic demand.
• If the Phase 1 demand ends while the Phase 5 demand still exists, the controller terminates Phase 1 and starts timing Phase 2, while continuing to time Phase 5. This potential sequence is indicated by the arrow that connects the 1 and 5 boxes with the 2 and 5 boxes. • If the Phase 5 demand ends while the Phase 1 demand still exists, the controller terminates Phase 5 and starts timing Phase 6, while continuing to time Phase 1. This potential sequence is indicated by the arrow that connects the 1 and 5 boxes with the 1 and 6 boxes. • If the Phases 1 and 5 demands end simultaneously, the controller terminates both phases at once and starts timing Phases 2 and 6.
Once the controller has advanced to the point where it is timing either Phases 1 and 6, or Phases 2 and 5, its only possible path is to further advance to serve Phases 2 and 6.
When the controller is ready to advance from one combination to the other, for example, from Phases 2 and 6 to Phases 3 and 7, it will always terminate the last two phases served in the combination together. For example, if Phases 2 and 6 are timing, and the Phase 6 demand ends, Phase 6 will remain green until Phase 2 is ready to terminate.
Phase timing in the second combination, consisting of Phases 3, 4, 7, and 8, proceeds in the same manner as described for the first combination.
If a phase does not have any demand during a cycle, the phase will be skipped and the remaining phases with demand will be serviced in accordance with the predefined paths.
The concurrent phase timing capabilities of the dual ring controller provide for great efficiency and flexibility in servicing traffic demand. However, when assigning vehicle phases, care must be taken that conflicting traffic movements are not allowed by phases that can time concurrently.
In Figure 11-5, there is an Exclusive Pedestrian Phase shown between Combinations 1 and 2. If a call is received for the Exclusive Pedestrian Phase while Combination 1 phases are timing, the Exclusive Pedestrian Phase will be serviced after the Combination 1 phases and before the Combination 2 phases in the cycle. If a call for the Exclusive Pedestrian Phase is received while Combination 2 phases are timing, the Exclusive Pedestrian Phase will not be serviced until after both the Combination 2 and Combination 1 phases complete their timing, unless there is no demand for Combination 1 phases, in which case the Exclusive Pedestrian Phase will be timed following the Combination 2 phases.
The Models 170/179 also provide for an option to change from the normal dual ring mode to a 6- phase sequential mode.
§11.3.3.1 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-137
Figure 11-5 shows the potential sequence of operation for the 6-phase sequential mode. In this mode, Combination 1 consists of Phases 1, 2, 5, and 6 and is served exactly as in the normal dual ring mode. The Exclusive Pedestrian Phase is also served as in the normal dual ring mode. However, in this mode, Combination 2 phases are sequenced such that concurrent phasing no longer exists. In the 6-phase sequential mode, Phases 3, 4, 7, and 8 will be serviced one at a time, in the preferred order indicated in Figure 11-5, assuming demand for each phase.
Figure 11-5 Phase Sequencing Relationships
Source: NYS TE&HS Traffic Actuated Processing System Operator’s Manual
3/15/02 §11.3.3.1 11-138 SIGNS, SIGNALS, AND DELINEATION
The number of phases required for the proper and efficient operation of a signalized intersection varies with the composition and direction of both vehicular and pedestrian flows as well as with the number of entering highways and driveways and the general intersection layout. As a general rule, the number of phases should be held to a minimum. Additional phases reduce the green time available for other phases. They may decrease intersection efficiency because of additional starting delays, additional change (yellow and all red) intervals, longer cycles, and adverse impact on optimal progression. In determining the number of phases required, the goals of safety and capacity may conflict. For example, in many situations, protected left-turn phases are safer than permitted left turns. However, the added phases may result in longer cycle lengths, reduced progression in the system, and increased delay and percent of vehicles stopping.
The usual traffic control signal will operate on a 2-phase cycle in which the right of way is alternately assigned to each of the two crossing movements. Table 11-14 shows an example of a 2-phase signal operation. Intersections having a large and concentrated volume of left turns or unusually heavy pedestrian movements, and intersections having more than 4 approaches for entering traffic, may require more than 2 phases in order to eliminate conflicts between vehicles or between vehicles and pedestrians. The division of the cycle into more than 2 phases should be avoided if at all possible since each additional phase introduces delays before the green interval is given to other phases.
The number of phases chosen is primarily a left-turning issue. In general, as left-turning volumes and opposing through traffic volumes increase, a point is reached where it is difficult for left-turning traffic to find safe and adequate gaps. A separate left-turn lane will alleviate the problem somewhat by providing storage space in which turning vehicles can wait for an acceptable gap in opposing traffic. Alternative solutions to installing a left turn phase may include prohibiting left turns entirely or reconstructing the intersection. Left turn prohibition should only be considered where convenient alternate routes exist. Left turns can be prohibited on a full- or part-time basis. The following should be taken into account when considering a left-turn prohibition:
• Volume and classification (type) of vehicles diverted. • Adequacy of marked or likely-to-be-utilized routes, (environmental considerations, pavement and bridge or culvert structural capacity, safety features, adjacent land use, etc.). • Transit routes. • Additional travel time and distance. • Enforcement needs (particularly during the initial week or two of change). • Will the prohibition solve the problem, or will it simply move the problem somewhere else.
§11.3.3.1 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-139
Table 11-14 Two-Phase Traffic Signal Operation Ped Crossing Ped Crossing Phase Main Street Side Street Main Street Side Street
Startup Phase Green Red DONT WALK DONT WALK
Phase 2 Green Red DONT WALK DONT WALK(1)
1st Clearance Yellow Red DONT WALK DONT WALK 2nd Clearance Red Red DONT WALK DONT WALK
Phase 4 Red Green DONT WALK(1) DONT WALK
1st Clearance Red Yellow DONT WALK DONT WALK
2nd Clearance Red Red DONT WALK DONT WALK
Flashing Flashing Flashing Inoperative Inoperative Operation Yellow Red Notes: 1. This indication will be WALK followed by a flashing DONT WALK and steady DONT WALK pedestrian clearance interval if a pedestrian push button has been actuated.
Another obvious, but generally cost-prohibitive, solution is to reconstruct the intersection. An interchange, roundabout, or a jug handle can eliminate the need for a left-turn phase.
There are no established warrants for left-turn phasing in the NYS MUTCD. Consideration should be given to a left-turn phase under the conditions that follow.
• The installation of a left-turn phase will improve the level of service and traffic operation of the intersection. • Delay - Install left-turn phasing, if a left-turn delay of 2 vehicle hours or more occurs in the peak hour on a critical approach. Also, there must be a minimum left-turn volume of 50 during the peak hour and the average delay for left-turning vehicles must be at least 35 seconds. These two provisions should both be met for appropriate left-turn phasing. • Volumes - Consider left-turning phasing when the product of the left-turning volume times the opposing volume during the peak hour exceeds 100,000 on a 4-lane highway or 50,000 on a 2-lane highway. The left-turn volume must also be at least 50 during the peak hour period. Volumes meeting these levels indicate that further study of the intersection is required. • Traffic conflicts - Consider left-turn phasing when a consistent average of 14 or more total left-turn conflicts or 10 or more basic left-turn conflicts occur in the peak hour. (The basic left-turn conflict occurs when a left-turning vehicle crosses directly in front, or blocks the lane of an opposing vehicle. The other left-turn conflicts occur when a second through vehicle following the first one also has to brake or when a vehicle turns left on red.) • Five or more left-turn accidents within a 12-month period.
Protected/permitted left-turn phasing is a left-turn movement of traffic at a signalized intersection
3/15/02 §11.3.3.1 11-140 SIGNS, SIGNALS, AND DELINEATION having a separate phase in the signal cycle to provide a protected (green arrow) phase as well as a nonprotected (circular green) phase. This can reduce the delay caused by addition of phases by allowing turns against the opposing flow where conditions permit. One of the basic precepts of the protected/permitted left-turn phasing technique is that the protected green arrow is displayed only when needed by traffic demand. It is therefore emphasized that the protected/permitted left-turn phasing technique is for efficiency as opposed to accident reduction (although it will probably offer safer operation than strictly permissive operation). Where left-turn phasing is needed primarily to increase left-turn capacity, consider the use of protected/permitted left-turn phasing before protected-only left-turn phasing is implemented.
Protected/permitted left-turn phasing should not be used when any of the following conditions exist:
• Protected-only phasing is currently in operation and the speed limit is over 35 MPH. • Left-turn movements must cross 3 or more opposing through lanes. • Intersection geometrics force the left-turn lane to have a separate signal head. • Double left-turn movements are allowed on the approach. • A left-turn accident problem exists (5 or more left-turn accidents in 12 months). • Stopping sight distance for the opposing through movement is nonstandard. • Sight distance for the left-turn movement is nonstandard. • Unusual geometrics, as at multilegged (5 or more approaches) intersections.
In general, for intersections with traffic volumes indicating a need for a separate left-turn phase, protected/permitted left-turn phasing will provide safer left-turn operations than permitted only left- turns, but will not provide the safety of a protected-only left-turn phase.
Leading and lagging left turns are two alternatives for inclusion of left turns in the signal phasing. A leading left-turn is one where the left-turn green arrow precedes the green indication for oncoming traffic. In contrast, the lagging left-turn phase provides the left-turn arrow following the green indication for oncoming through traffic. There are no specific guidelines in the NYS MUTCD for when to use leading or lagging left-turn phases. The following should be considered when determining left-turn operation.
• Generally, on 2-lane roads without an exclusive left-turn lane, a leading left-turn phase is preferred. A leading left-turn phase on a 2-lane road will reduce traffic congestion by clearing the left-turning vehicles through the intersection first. • Lagging left-turn phasing is the preferred operation at T-intersections. • Consider uniformity with the left-turn operation at nearby signals. If all the nearby signals have leading left-turn phases, than a leading left-turn phase may be appropriate. If all the nearby signals have lagging left-turn phases, a lagging left-turn phase should be considered. • If the signal is part of an interconnected signal system, consider how well the left-turn operation will fit into the progression. • When the signal controller is ready to advance from one combination to the other, for example, from Phases 2 and 6 to Phases 3 and 7, it will always simultaneously terminate the last 2 phases served in 1 combination. For example, if Phases 2 and 6 are timing, and Phase 6 demand ends, Phase 6 will remain green until Phase 2 is ready to terminate. • Movements requiring the greater amount of green time should be assigned to the last
§11.3.3.1 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-141
phases in each combination (Phases 2, 6, 4, and 8) to take advantage of this additional green time a phase may receive.
Table 11-15 shows the advantages of leading and lagging left-turn signal operation while Table 11-16 shows the disadvantages.
Table 11-15 Advantages of Lead and Lag Left-Turn Operation ADVANTAGES OF LEAD ADVANTAGES OF LAG
1. Permits higher intersection capacity on 1. Both directions of straight through traffic restricted width roadways, compared start at the same time. with 2-phase traffic signal operation. 2. Approximates the normal driving behavior 2. Reduces traffic congestion by clearing of vehicle operators. the left-turning vehicles through the intersection first. 3. Provides for vehicle/pedestrian separation as pedestrians usually cross 3. Desirable where left-turn lanes do not at the beginning of through green. exist. 4. Where pedestrian indications are used, 4. Can be used to provide progressive pedestrians have cleared the intersection traffic movement in an interconnected by the beginning of the lag-green interval. signal system with unequal spacings. 5. Cuts off only the platoon stragglers from 5. Minimizes conflicts between left-turn and adjacent interconnected intersections. opposing through vehicles by clearing the left-turn vehicles through the intersection 6. Less time needed for the lag, since left first. turns can filter through the opposing gaps during the time the through 6. Drivers tend to react quicker than with indications are exhibited. lag-left operation. 7. Can be used to provide coordinated 7. Opposing through traffic has been progressive traffic movement in an previously stopped when the left turns interconnected signal system with start. unequal spacings.
3/15/02 §11.3.3.1 11-142 SIGNS, SIGNALS, AND DELINEATION
Table 11-16 Disadvantages of Lead and Lag Left-Turn Operation DISADVANTAGES OF LEAD DISADVANTAGES OF LAG
1. Left turns at end of leading indication 1. Creates conflicts for opposing left turns may preempt the right of way from at start of lag interval as opposing left- opposing movements when the green is turn drivers expect both movements to exhibited to the stopped opposing stop at the same time. movement. 2. Where there is no left-turn lane, an 2. Opposing movements may make a false obstruction to the through movement start in an attempt to move with the during the initial green interval is created. leading green vehicles movement. 3. A left green arrow cannot be displayed 3. May create vehicle/pedestrian conflict during the circular yellow, therefore, a during the leading green interval. stop-start situation is necessary with simultaneously opposing left turns.
4. When used on only one approach, pedestrians desiring to cross the opposite approach may assume that both approaches have a red indication.
Figure 11-6 and Table 11-17 show a signalized intersection with leading protected/permitted left-turn phases on the major street and lagging protected/permitted left-turn phases on the side street. Figure 11-7 and Table 11-18 show a signalized intersection with leading protected-only left-turns phasing on the side street and lagging protected-only left-turn phasing on the major street.
In the protected/permitted example in Figure 11-6 and Table 11-17, note the use of the right green arrow on face 6 during Phase 1 and on face 8 during Phase 5. This operation is provided in Models 170/179 by the overlap feature. The overlap feature is used to allow traffic movement during 2 or more vehicle phases. Right-turn overlaps may be used when the right-turn movement would not conflict with vehicular or pedestrian traffic moving on an adjacent street and an acceptable traffic operation would be provided.
§11.3.3.1 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-143
Figure 11-6 Signalized Intersection with Protected/Permitted Left-Turn Phasing
3/15/02 §11.3.3.1 11-144 SIGNS, SIGNALS, AND DELINEATION
Table 11-17 Signalized Intersection with Protected/Permitted Left-Turn Phasing FACES
PHASE 12345678
Startup Green Green Green Green Red Red Red Red
1 Red Red Red Red Red Red Red Red LGA RGA 2 Red Red Green Green Red Red Red Red
5 Red Red Red Red Red Red Red Red LGA RGA
6 Green Green Red Red Red Red Red Red
1 + 5 Red Red Red Red Red Red Red Red LGA LGA RGA RGA
1 + 6 Green Green Red Red Red Red Red Red LGA RGA
2 + 5 Red Red Green Green Red Red Red Red LGA RGA
2 + 6 Green Green Green Green Red Red Red Red
3 Red Red Red Red Green Green Red Red
4 Red Red Red Red Red Red Red Red LGA
7 Red Red Red Red Red Red Green Green 8 Red Red Red Red Red Red Red Red LGA
3 + 7 Red Red Red Red Green Green Green Green
3 + 8 Red Red Red Red Green Green Red Red LGA
4 + 7 Red Red Red Red Red Red Green Green LGA
4 + 8 Red Red Red Red Red Red Red Red LGA LGA
Flash Yellow Yellow Yellow Yellow Red Red Red Red
Key: LGA = Left Green Arrow RGA = Right Green Arrow
§11.3.3.1 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-145
Figure 11-7 Signalized Intersection with Protected Left-Turn Phasing
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Table 11-18 Signalized Intersection with Protected Left-Turn Phasing F A C E S
PHASE 1 2,3 4 5,6 7 8,9 10 11,12
Startup LRA Green LRA Green LRA Red LRA Red
1 LRA Red LRA Green LRA Red LRA Red 2 LGA Red LRA Red LRA Red LRA Red
5 LRA Green LRA Red LRA Red LRA Red
6 LRA Red LGA Red LRA Red LRA Red
1 + 5 LRA Green LRA Green LRA Red LRA Red
1 + 6 LRA Red LGA Green LRA Red LRA Red
2 + 5 LGA Green LRA Red LRA Red LRA Red
2 + 6 LGA Red LGA Red LRA Red LRA Red
3 LRA Red LRA Red LRA Red LGA Red 4 LRA Red LRA Red LRA Green LRA Red
7 LRA Red LRA Red LGA Red LRA Red
8 LRA Red LRA Red LRA Red LRA Green
3 + 7 LRA Red LRA Red LGA Red LGA Red
3 + 8 LRA Red LRA Red LRA Red LGA Green
4 + 7 LRA Red LRA Red LGA Green LRA Red
4 + 8 LRA Red LRA Red LRA Green LRA Green
Flash Dark Yellow Dark Yellow Dark Red Dark Red
Key: LRA = Left Red Arrow LGA = Left Green Arrow
Another example of an overlap is shown in Figure 11-8a and Table 11-19. This example shows 2 offset intersections operated from one traffic signal controller with a 3 phase operation. Faces 3 and 4 display a green indication during both Phase 1 and Phase 4, while faces 7 and 8 display green indications during Phases 1 and 3. This operation is provided by programming the Models 170/179 overlap feature to allow green indication on faces 3, 4, 7, and 8 during the required phases. This operation would be used at closely spaced intersections with limited storage space between the intersections. As either side street receives a green indication, it is allowed to move through the
§11.3.3.1 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-147 adjacent intersection. This operation also provides permitted/protected left turns from the artery to the side streets. If there were detectors located between the intersections the Model 179 controller software detector switching function could be used to provide the appropriate operation. The detector located in the eastbound lane between the intersections could be programmed to be associated with Phase 1 during Phase 1 and Phase 3 during Phase 3. This detector could also be turned off during Phase 3.
Figure 11-8a Offset Intersection with Three-Phase Operation
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Table 11-19 Operation for Offset Intersections with Three-Phase Operation F A C E S
Phase 1,2 3 4 5,6 7 8 9,10 11,12
Startup Green Green Green Red Green Green Green Red
1 Green Green Green Red Green Green Green Red Clear to Yellow Yellow Yellow Red Green Green Yellow Red 3
Clear to Yellow Green Green Red Yellow Yellow Yellow Red 4
3 Red Red Red Green Green Green Red Red LGA
Clear to Red Red Red Yellow Yellow Yellow Red Red 4 LYA
Clear to Red Red Red Yellow Green Green Red Red 1 LYA
4 Red Green Green Red Red Red Red Green LGA
Clear to Red Green Green Red Red Red Red Yellow 1 LYA
Clear to Red Yellow Yellow Red Red Red Red Yellow 3 LYA
Flash Yellow Yellow Yellow Red Yellow Yellow Yellow Red
Key: LGA = Left Green Arrow LYA = Left Yellow Arrow
§11.3.3.1 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-149
Figure 11-8b Offset Intersection with Two Phases and Double Clearance
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If the intersections shown in Figure 11-8b were operated as a 2-phase signal from one controller, one phase being the artery movements and the second phase being the movements for both side streets, there may be a problem with storage for vehicles between the intersections. This problem can be overcome by use of a double clearance following the artery phase. Table 11-20 shows this operation.
Table 11-20 2-Phase Operation with Double Clearances F A C E S Phase 1,2 3,4 5,6 7,8 9,10 11,12
Startup Green Green Red Green Green Red
2 Green Green Red Green Green Red
1st Yellow Green Red Green Yellow Red Clearance
2nd Red Green Red Green Red Red Clearance 3rd Red Yellow Red Yellow Red Red Clearance
4th Red Red Red Red Red Red Clearance
4 Red Red Green Red Red Green
1st Red Red Yellow Red Red Yellow clearance
2nd Red Red Red Red Red Red Clearance
Flash Yellow Yellow Red Yellow Yellow Red
All four parts to the double clearance may not be required depending on the time needed to clear the vehicles between the intersections, the width of the intersection area, and the desired operation. For example, the 4th clearance may not be needed if the intersection area can be cleared in 3 seconds or less, or faces 3, 4, 7, and 8 could be yellow during the 2nd clearance, thereby eliminating the need for the third clearance. This operation would be possible if the 1st and 2nd clearances provided sufficient time for vehicles to clear from between the intersections.
Earlier, it was stated that the Models 170/179 controller provided a 6-phase sequential mode of operation. Figure 11-9 shows a multileg intersection using the 6-phase sequential mode of operation. Due to heavy left turn movements from the side roads, a separate phase was required for each side road. The 5th leg of the intersection also required a separate signal phase. The table of operation for this intersection is shown in Table 11-21.
§11.3.3.1 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-151
Figure 11- 9 Intersection Requiring Six-Phase Sequential Mode of Operation
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Table 11-21 6-Phase Sequential Mode of Operation F A C E S Phase 12345678910
Startup G G G G R R R R R R
1GGRRRRRRRR 5RRGGRRRRRR
6RRRRRRRRRR LGA
1 + 5GGGGRRRRRR
1 + 6 G GRRRRRRRR LGA
3RRRRRRGGRR LGA
4RRRRGGRRRR LGA
7RRRRRRRRGG
Flash Y Y Y Y R R R R R R
KEY: G=Green, LGA = Left Green Arrow, R = Red
11.3.3.2 Emergency Vehicle Phasing
See Sections 11.3.1.11 Emergency Vehicle Signals and 11.3.3.5 Model 179 Timeclock and Programmable Features.
11.3.3.3 Pedestrian Phasing
The Models 170/179 traffic signal controller has pedestrian timing for each phase built into the software. The pedestrian timing feature is designed to reject multiple pedestrian detector actuations, so that only one pedestrian actuation is registered per cycle and vehicle timing is extended only by vehicles. In addition to pedestrian push buttons at signals where pedestrian indications are used, push buttons and pedestrian timing should be installed at all traffic signals where pedestrians are present and may cross the roadway. See Section 11.3.1.4 Pedestrian Signals.
11.3.3.4 Type of Traffic Signal Operation (Pretimed, Semi-Traffic-Actuated, or Full-Traffic-Actuated)
§11.3.3.4 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-153
There are two basic types of traffic signal operation; pretimed operation and actuated operation. Early signal operations were primarily pretimed, where a fixed sequence of intervals of fixed duration was used to assign the right of way. In the late 1920s, an advance was made that permitted the signal controller unit to respond to actual traffic demands, and the application of traffic-actuated control began. Through the years, traffic-actuated control grew to include semi-actuated operation, full-actuated operation and volume-density control. New York State’s Models 170/179 traffic signal controller can provide any of these operations.
A. Pretimed Operation
Pretimed operation provides a fixed sequence of right of way assignments (phases), each of a fixed duration and regularly repeated. Both the cycle length and phase intervals are established by a predetermined time schedule and are of a fixed length. This type of operation does not respond to actual traffic demands and cannot skip a phase which may have no demand. Although regularly repeated, this fixed timing can be varied on a time-of-day (scheduled) basis, by operator command, or in response to variable-measured traffic patterns.
The major elements of pretimed operation are:
• Fixed number and sequence of phases. • Fixed phase and interval lengths. • Fixed cycle length. • Not responsive to traffic.
This type of signal operation is used at intersections where traffic volumes and patterns are stable and predictable. It may also be used at intersections included in a coordinated signal system where traffic progression is required on more than one phase and the needs of progressive movement are such that allowing the early return of the coordinated phase green, as may happen with actuated operation, would result in unnecessary vehicle stops. For example, pretimed operation is desirable at closely spaced intersections where complex phasing is used and precise interval timing is critical to efficient platooning of various traffic movements.
In New York State, pretimed operation is generally used only in coordinated signal systems in urban areas. Pretimed operation generally is not used at isolated traffic signal locations.
B. Semi-Traffic-Actuated Operation (STA)
Actuated operation provides variable vehicular and pedestrian timing and phasing intervals which depend on traffic volumes or the presence of pedestrians. The presence of traffic is determined by vehicular detectors or pedestrian actuation of push buttons. With semi-actuated operation, one phase (usually the major street) operates in the nonactuated mode.
In semi-actuated operation, the major street has a green indication at all times, until detectors on the minor street determine that a vehicle has arrived. Semi-actuated operation provides a
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guaranteed minimum green time for the nonactuated phase. Right of way is given to the actuated phase only when an actuation call is placed for the phase. After timing the appropriate clearance intervals (yellow and all red), a green is given to the actuated phase for the initial period. The actuated phase being timed will retain the right of way as long as vehicles are detected and the gap timer is reset. The green will end when either the vehicle interval is allowed to time out or the preset maximum green time has been reached. In either case, the clearance intervals are timed and right of way is given to the next actuated phase with a call or returned to the nonactuated phase. If the actuated phase was terminated by reaching the maximum green setting, a vehicle call is placed for that phase when its clearance interval is entered.
The major elements of semi-actuated operation are:
• Detectors are only on minor street approaches. • Major street has a set minimum green interval guaranteed. • Green for major street extends indefinitely until interrupted by minor street actuation. • Minor street phase receives green after actuation after major street phase has completed its minimum green interval. • Minor phase has minimum initial green period. • Additional actuations will extend minor phase green until preset maximum is reached or a gap in actuations greater than the set gap timer occurs. • Green will be returned to actuated phase if it was terminated by reaching the maximum setting.
Semi-traffic-actuated (STA) operation is used at the intersection of arterial streets with a side street having relatively moderate and irregular vehicle and pedestrian traffic. Semi-actuated operation is also used at signals which are to be coordinated with signals at adjacent intersections. This operation would also be used in coordinated signal systems where early return of the coordinated phase green is not of concern.
C. Full-Traffic-Actuated Operation (FTA)
This type of operation requires detectors on all approaches to the intersection. The major difference between full- and semi-actuated operation is that right of way does not return automatically to a designated phase under the full-actuated operation (FTA controllers may be programmed to return to a given phase by programming the memory/recall status for the phase to minimum recall). With FTA operation, main street green varies with demand rather than being a preset minimum. The green will remain on the phase last serviced until demand is registered for a conflicting phase, unless recalled elsewhere. Once a call for a conflicting phase has been received the phase timing green may remain green up to the programmed maximum green time. The maximum green time does not begin timing until there is a call for a conflicting phase. Accordingly, a phase may remain green for some time before it starts timing its maximum green. Depending on the detector activity for the green phase, the controller may or may not service the opposing phase immediately upon receipt of a demand.
The major elements of full-actuated operation are:
§11.3.3.4 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-155
• Detectors on all approaches. • Each phase has a preset initial interval to provide the starting time for standing vehicles. • Green interval is extended by preset gap time for each actuation after the initial interval has completed timing, provided a gap greater than the initial interval does not occur. • Green extension is limited by preset maximum limit (Models 170/179 have 3 maximum greens per phase selectable by time of day). • Each phase has 3 choices for its recall setting.
The 3 recall setting options are discussed below.
1. Off Green will remain on last-called phase when no demand is indicated on the other phases.
2. Minimum Recall A call is automatically placed for the phase after it is served. The controller will cycle to, and serve phases in, the “minimum recall” mode in each cycle, for at least the initial interval plus any vehicle-actuated minimum green period. When in this mode, the controller will continue to accept vehicle actuations for the phase, and will time related variable initial, extension periods, and pedestrian timing.
3. Pedestrian Recall When pedestrian recall is on, a permanent demand for pedestrian service is placed for the associated phase(s). The controller will cycle to and serve phases in the “pedestrian recall” mode each cycle, for a minimum time interval equal to the pedestrian “WALK” plus pedestrian clearance intervals. When in this mode, all vehicle-related phase timing will take place concurrently with pedestrian timing in the normal manner, except that the green interval will never be less than the minimum pedestrian timing.
Full-traffic-actuated operation is generally used when the intersection operates independently and where demand on all approaches varies throughout the day. Complicated intersections where several conflicting movements must be handled separately often require this type of operation to permit a reasonable degree of operating efficiency. FTA operation should be used at most intersections which are not included in a coordinated signal system.
Models 170/179 also provide volume density features which may be used with all actuated phases. In the volume density mode of operation, the controller is programmed to operate with a variable initial interval and a reducible gap, in addition to the timing features of the normal actuated phase. These added features vary the amount of time a phase will receive the right of way based upon more complex evaluation of traffic conditions. The maximum extension for a phase functions the same as for a normal actuated phase. The initial interval is normally the time required for a standing queue between the detector and the stop line to get started and move into the intersection. With volume density control, detectors are placed a longer distance from the stop line (see Table 11-13 for detector placement). To avoid long preset initial intervals, the volume density module counts the number of vehicles arriving during the red phase and expands the initial interval if necessary as per variable initial time. Gap time is measured as the time between actuations by successive vehicles. The controller is set to
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terminate the green indication if the length of the measured gap exceeds a set duration. It is desirable for the maximum gap time to approximate the time it takes for a vehicle to travel from the detector to the intersection. This interval must be fairly long because of the distance involved which, in turn, results in inefficient operation. The allowable gap may be reduced to a preset minimum based upon waiting time of vehicles on other phases as per programmed time to reduce and minimum and maximum gap values.
The major elements of volume density operation are:
• Detectors are placed on all approaches. • Each volume density phase has a variable initial time. • The gap time is the extended green time created by each additional actuation (this time is set as that required to travel from the detector to the stop line). • The gap time is reduced to a minimum gap after a preset time. • The green extension is limited by preset maximum limit (Models 170/179 software has 3 maximum greens per phase selectable by time of day).
Volume density operation can be effective at intersections when high speeds and high volumes are found. To achieve efficiency, the detector must be carefully located and the proper timing must be installed on the controller.
11.3.3.5 Model 179 Time Clock and Programmable Features
A detailed list and description of all Model 179 time clock and programmable features may be found in the Traffic Engineering and Highway Safety Division’s Traffic Actuated Processing System (TAPS) Operator’s Manual. This section will discuss the features that a designer should be aware of when designing a traffic signal’s operation and installation.
A. Time Clock Functions
The Model 179 TAPS program provides 8 separate functions that may be turned on or off based on time of day, day of week, and week of year. These functions are known as time clock functions and include the following:
• Flashing Operation. • Phase Omit A. • Phase Omit B. • Rest in Red. • Maximum Green II. • Maximum Green III. • Input by time clock. • Auxiliary Output (SP 9Y).
A.1 Flashing Operation. This function is used when the traffic signal is to operate as a flashing
§11.3.3.5 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-157
signal during a predetermined time period. This operation is often used at permit traffic signals at shopping centers or other locations where the signal may not be needed on a full time basis. It should be noted that this flashing operation is done completely by software, and is not performed by any flasher relay in the cabinet, nor is it related in any way to the signal emergency flashing operation.
Transition of the signal from 3-color to flashing operation takes place as follows:
• Calls for all phases not currently timing are removed. • Phases currently timing will complete their minimum green timing and then cycle to an all red condition through normal clearances. • The signal will commence flashing operation.
Transition of the signal to 3-color operation upon termination of the flashing operation takes place by one of two means.
• If a start-up sequence is programmed for the signal operation, the signal will sequence through the standard start-up sequence. • If no start-up sequence is programmed for the signal, the signal will freeze its programmed flashing display for 4 seconds, and will then display all red indications, before displaying green indications allowed in the normal signal operation. The length of the all red indications is programmable from 4 seconds to 12 seconds (default 8 seconds).
Following both of the above transitions to 3-color operation, calls will be placed for all allowed phases.
A.2 Phase Omit A and B. These features are used to omit or allow a traffic phase on a time clock basis. There are 2 separate Phase Omit features available. Each Phase Omit is completely independent, and any combination of phases may be programmed into either Omit. The two Omit functions may be used singularly or in any combination during any part of the day. This feature could be used at intersections where a left-turn phase might only be needed during the peak period or where a left-turn movement is prohibited during the peak period and the left- turn phase needs to be omitted.
A.3 Rest-In-Red. If a phase is programmed for Rest-In-Red mode and completes its appropriate vehicle and/or pedestrian phase timing without any calls being made for opposing phases, the phase will cycle into a red condition and will remain there waiting to immediately service the next call for an appropriate phase. Any phases that are not programmed to Rest-in- Red will rest in green, and will have to serve at least one gap time after receipt of an opposing call, before sequencing through its clearance(s) to serve an opposing phase. The benefit of this type of operation is that when all indications are red, no clearance interval is required upon the first detector actuation.
The rest-in-red feature allows programmed phases to rest-in-red on a timeclock basis. Any
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combination of phases may be programmed to rest-in-red. If all phases are set to rest-in-red, all indications will be red after the called phase has cycled to red. Upon a new actuation, the phase associated with the detector begins immediately by having the red indication promptly change to green. Rest-in-red is sometimes used as a speed control measure during periods of moderate to light traffic. Rest-in-red is not commonly used as there have been some problems with drivers becoming accustomed to getting the instant green and not slowing down when another phase actually has a green indication.
A.4 Maximum Green II and III. This feature allows the use of alternate Maximum Green Timing intervals on selected phases on a time clock basis. Two separate alternate Maximum Greens are provided. Any combination of phases may be programmed to use the Maximum Green II and III timers. Under normal conditions, the signal will use the timings set in the Maximum Green I timer. When the Maximum Green II and/or III time clock function becomes active, the signal will use the time set in the appropriate Maximum Green timer for those phases programmed. Phases not programmed for these functions will remain in their normal Maximum Green I timing mode. Maximum Green II and III mode may be used singularly or in any combination throughout the day. This feature is not something the designer needs to be concerned about since the timing of signals is done by the Regional Traffic Engineering Group.
A.5 Input by Time Clock. This feature allows any pair of the controller’s first 28 input positions to be turned on or off on a time clock basis. Any of these 28 input positions may be defined to perform any appropriate input functions. Accordingly, this function allows any input feature to be controlled on a time clock basis. Note that the inputs must be controlled in pairs (e.g., inputs 3 and 4). These pairs correspond directly to the grouping of such in the dual input rack positions of the Model 330 cabinet, and, in effect, the feature actually controls a cabinet rack position by time clock. The model 330 input groupings are inputs 1 and 2, 3 and 4, 5 and 6, etc. Accordingly, if the controller was programmed to control inputs 2 and 3 by time clock, inputs 1, 2, 3, and 4 would be controlled. Any combination of inputs may be controlled by timeclock, however, it should be noted that all are controlled by a single time clock and will turn on or off at the same time. This feature could be used to turn a detector off during the peak hour or to allow a bus preemption only during the peak hour.
A.6 Auxiliary Output (SP 9Y). This feature makes it possible to turn the Switchpack 9 yellow output on or off via time clock. This feature would be used to turn an illuminated sign on or off during programmed periods of the day. An example would be an intersection with a left-turn prohibition during the peak hour. This feature could be used to turn the NO LEFT TURN sign on and off.
B. Startup Display and Phasing
The Model 179 will go through a startup sequence every time the controller is restarted, upon power-up after a power-down of 2 seconds or longer, or when it comes out of flashing
§11.3.3.5 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-159
operation. As part of the startup sequence, calls are placed for all vehicle phases allowed. If a power-down lasts less than two seconds, the controller will start at the exact point in the signal operation where the power failure occurred.
The NYS MUTCD [Section 272.16 (c) (4)] states that “Preplanned automatic changes from flashing to stop-and-go operation should be made at the beginning of the artery green interval where practicable, preferably at the beginning of the common green interval (i.e., when a green indication is shown in both directions on the artery). Preplanned automatic changes from stop- and-go to flashing operation should be made at the end of the common artery red interval where practicable (i.e., when a red indication is shown in both directions on the artery). Emergency changes from stop-and-go operation to flashing operation (e.g., when a display of conflicting green indications is sensed by the control equipment) may occur at any time”.
The Model 179 startup sequence is a user-programmable sequence consisting of a 2-part startup display and the startup phases. Accordingly, the designer should indicate in the Table of Operation any required startup display and the startup phases. If a startup display is used, the startup phases must also be programmed into the controller. If startup phases are not programmed, then the controller will go through a default startup consisting of an 8-second all red, followed by the display and timing of the 1st phase, or 2 concurrent phases, allowed in the normal signal cycle.
C. Input Functions
The NYS Model 330 pole-mounted controller cabinet is capable of receiving up to 28 channels of input, each of which is programmable by function and capable of extensions and delays. The inputs are connected to the cabinet at the terminal block and are interfaced to the Model 179 controller through one of the following modules.
• Loop Vehicle Detector Module • Magnetic Detector Amplifier Module • Magnetometer Vehicle Detector Module • D.C. Isolation Module • A.C. Isolation Modules
Each input may be programmed to provide one of the following functions subject to the pairing of inputs as discussed under Input by Time Clock.
• Normal Vehicle Detector • Vehicle Calling Detector • Pedestrian Push Button
A call for one of these functions will result in the appropriate vehicle or pedestrian demand being placed. A vehicle-calling detector is different from a normal vehicle detector in that it will only place a call during the yellow or red of the phase it is associated with, and can place only one call each cycle.
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C.1 Exclusive Pedestrian. A call for this function will result in the exclusive pedestrian phase being serviced.
C.2 Preemption A, B, or C. Preemption is the interruption of normal vehicle and pedestrian timing and sequencing to service a special predefined preemption signal operation. The Model 179 controller provides 3 separate preemption operations, A-C. The preemption operations are briefly described below:
Preempt A. This is a preemption that interrupts normal signal operation as quickly as safely possible to sequence directly to the preemption operation. This preemption is generally used to accommodate those preemptions which require service as soon as possible. See Section 11.3.1.11 Emergency Vehicle Signals for additional discussion on operation of Preemption A.
Preempt B. This preemption allows the signal to complete its timing for the phases currently active in a normally actuated manner, after which it will sequence directly to the preemption operation. Accordingly, it is used for preemptions that require priority service, but can wait for such. This preemption could be used for bus priority operation.
Preempt C. This preemption is like Preempt A in that it interrupts normal signal operation as rapidly as safely possible. However, Preempt C allows the user to define one or two concurrent phases that will be serviced immediately prior to the preemption operation. Preempt C is generally used for railroad preemptions where it is desired to clear a signal approach that is crossed by the railroad track, before cycling to the preemption operation. Preempt C is unique in that it also has an option to provide flashing operation as the preemption operation.
See the Traffic Engineering and Highway Safety Division’s Traffic Actuated Processing System Operator’s Manual for additional details on the operation of these preemptions.
C.3 Phase Selection A, B, C, or D. This function provides for priority servicing of selected phases based upon input from an external device. The Model 179 provides 4 separate Phase Selection options A - D, each of which is controlled by a separate input and serviced separately. Any 1 or combination of up to 4 Phase Selections can be used in a signal operation. This function could be used to provide bus priority or used with a queue detector to detect spillback onto the mainline of a freeway.
§11.3.3.5 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-161
C.4 Detector Delays and Extensions. Detector delays and/or extensions may be used on any of the 28 inputs. If an input is assigned a delay time, the controller will time the appropriate delay timer before recognizing and acting upon a call from the input. In effect, the controller will act as though the call has not been received until the delay timer expires. The delay timer starts as soon as the call is received. Since the controller does not act upon the call until the delay timer expires, the call will be forgotten if it goes away before the delay timer expires. One use of detector delay would be on a highway without a left-turn lane. A detector would be installed in the through/left-turn lane and would be programmed with a delay. If a vehicle remained in the detection zone longer than the delay, a left turn phase could be called by the controller. Another use of a detector delay would be on a force-off loop for an off ramp. If a vehicle stopped in the detection zone the controller would call the ramp phase or a preemption phase to clear the ramp before traffic backs up on the main line.
If an input is given an extension time, the controller will hold the input active for the amount of time set in the extension timer. In effect, the controller will act as though the call has not gone away until the extension timer expires. The extension timer starts as soon as the call is removed. The timer is reset with each subsequent actuation. An extension timer could be used in a combined point and presence detection system. The extension timer would hold the call while the vehicle traveled from the point detector to the presence detector. See section 11.3.2.2.C.3 for the benefits of this type of operation.
The above delay and extension timers may be used on any of the 28 inputs, regardless of the function of the input. Under normal circumstances, all detector delays associated with either normal vehicle detectors or calling detectors will operate only when the phase that the detector is associated with is either yellow or red. Detector delays for these detectors are inhibited during the associated phase green. Also, under normal circumstances, detector extensions associated with either normal vehicle detectors or calling detectors will operate only when the phase that the detector is associated with is green. Detector extensions for these detector types are inhibited during the associated phase yellow or red. This is known as green gating the delay and extension feature for these detector types. This function may be modified such that all detector delays and extensions associated with either normal vehicle detector inputs or calling detectors operate at all times regardless of the signal. This is known as unconditional delays or extensions.
C.5 Detector Jumping and Detector Switching. This function of the Model 179 allows the assignment of a “secondary” function to any of the first 8 detector input locations. Any valid input function can be used as a secondary function. There are two variations of this function as follows:
Detector Jumping - This variation allows an input to be programmed such that it will operate as both the normal function and the secondary function all the time. This mimics taking one input with one function and physically jumping it to another input with a different function.
Detector Switching - This variation allows the input to be programmed such that it will operate as either the normal function or as the secondary function depending upon which phase is timing. This allows the detector to “switch” function during the signal cycle. It should be noted
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that for detector jumping/switching, the calls to the secondary function will be subject to any delay and/or extension timing that is programmed for the normal function.
Refer to Figure 11-10 for the following examples of Detector Jumping/Switching.
Example A - It is desired to ensure that if either Side Street gets a call, then the opposite approach will also get a call. In this example, Detector number 4 would be programmed as a Phase 4 normal vehicle detector and would be programmed for detector jumping with a secondary function of Phase 8 calling detector. Detector 8 would be programmed as a Phase 8 normal vehicle detector and programmed for detector jumping with a secondary function of Phase 4 calling detector. When Detector 4 on the north Side Street (Phase 4) is actuated, a call will be placed for Phase 4 and a call will be placed for Phase 8, if Phase 8 is not timing a green interval. Since the secondary function for Detector 4 is a calling detector, no call will be placed for Phase 8 if a call is received when Phase 4 is timing a green interval. Calling detectors only place a call when the associated phase is not timing a green interval. A call will be placed if the associated phase is timing a clearance interval. Detector 8 would operate in a similar manner with a call being placed for Phase 4 when Phase 4 is not timing a green interval.
Example B - Traffic in the right turn lane (Detector 4) of the southbound Side Street normally calls Phase 1. It is desired to have this traffic extend Phase 4 whenever Phase 4 is timing green instead of calling Phase 1 during Phase 4. This is a case of detector switching. Detector 4 should be programmed as a normal vehicle detector and programmed for detector switching with a secondary function of Phase 4 normal vehicle detector. During Phase 2 and/or Phase 5, Detector 4 will operate as a normal Phase 1 vehicle detector placing calls for Phase 1. During Phase 1, this detector will also operate as a normal Phase 1 vehicle detector extending Phase 1. During Phase 4, Detector 4 will operate as a Phase 4 detector with vehicle calls extending Phase 4.
C.6 Coordination Inputs. These inputs allow the Model 179 to input Free, Offset, Synch and Cycle, via an AC Isolation Module in the input rack. These inputs are used with interconnection and coordination. See Section 11.3.3.5.F for a discussion of interconnection and coordination considerations.
All input assignments should be shown on the plans and in the Table of Input Wiring.
§11.3.3.5 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-163
Figure 11-10 Detector Jumping/Switching
D. Output Functions
The NYS Model 330 controller cabinet outputs the appropriate vehicular indications, pedestrian indications, illuminated signs, etc., through the use of up to 14 switch packs. Each switch pack consists of 3 solid state switches for opening and closing connections between electrical power and the traffic control device. It is by turning on or off the individual switches in the switch pack that the controller controls the appropriate output indications. Because the switch pack is most
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often used to control vehicle indications, the individual switches are referred to as the red, yellow, and green switches. However, as will be shown, the actual traffic control device turned on by the switch does not have to be the red, yellow, and green of the traffic signal head.
In general, each active switch pack should have only one switch on at any given time; either the green, the yellow, or the red. The red switch is turned on as the default position. The green and yellow switches will be turned on subject to the Programmable Features selected in the Model 179 controller and normal phase sequencing and timing.
The function of each switch pack is programmable into any one of seven general categories and should be shown in the Table of Switch Packs.
D.1 Vehicular Phase. A switch pack can perform the function of any one of the 8 vehicular phases. In general, a switch pack assigned as a vehicular phase will be red at all times except when that phase is active, during which time it will be green, yellow, or red in accordance with appropriate phase timing. The associated phase should be shown in the function column of the Table of Switch Packs.
D.2 Pedestrian Indications. Any switch pack can perform the function of any of the 6 user- defined pedestrian outputs. If pedestrian indications are desired for any of the pedestrian intervals permitted, the pedestrian interval must have a separate switch pack assigned for it. However, if it is only desired to have pedestrian timing associated with a phase, and no pedestrian indications are required, a switch pack output is not necessary and should not be designated in the Table of Switch Packs.
In general, a pedestrian switch pack output will display a steady or flashing WALK indication during the appropriate pedestrian timing interval, a flashing DONT WALK indication during the pedestrian clearance interval, and a steady DONT WALK at all other times. The WALK indication output is controlled by the green switch in the switch pack. The flashing and steady DONT WALK indications are controlled by the red switch. The yellow switch is not used for output for pedestrian indications.
D.3 Overlap Function. Any switch pack can perform the function of any of the 6 user-defined overlap outputs. The overlap feature is used to allow traffic movement during 2 or more vehicle phases. An overlap switch pack is like a vehicular phase switch pack in that it will cycle vehicular indications green-yellow-red. However, an overlap switch pack must be associated with one or more “parent” vehicle phases. Whenever any of the “parent” vehicle phases are green, the overlap switch pack will also display a green.
An overlap switch pack will normally display the appropriate yellow and red clearances with the “parent” phase whenever the “parent” phase is timing a clearance. However, because an overlap switch pack allows for the movement of traffic on 2 or more phases, it may be desirable to display the overlap switch pack green during the clearance when the signal is cycling from a phase that allows a certain traffic movement to another phase that also allows that traffic
§11.3.3.5 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-165
movement. The phases associated with the overlap switch pack should be shown in the Table of Switch Packs. For example, in Figure 11-6 and Table 11-17, the right green arrow on face 8 is an overlap of Phases 5 and 7. However, the right green arrow should not be displayed during phase 7. This overlap should be shown on the Table of Switch Packs as an overlap of “Phase 5 + Phase 7 - Phase 7 green” (N5 + N7 - N7G).
D.4 Double Clearance. Any switch pack can perform the function of any of the 6 user-specified double clearances. The double clearance feature is generally used to obtain an offset clearance between signal heads controlled by the same vehicular phase. A double clearance switch pack is like a vehicular phase switch pack in that it cycles vehicular indications green- yellow-red. However, a double clearance switch pack must be associated with one or more “parent” vehicle phases. Whenever the “parent” vehicle phase is green, the double clearance switch pack will also display a green. The “parent” phase for the double clearance switch pack should be shown in the Table of Switch Packs. Whenever the “parent” vehicle phase goes through a clearance, the double clearance switch pack will remain green while the “parent” phase is timing and displaying its yellow and red clearance intervals. Immediately following completion of those intervals, the double clearance switch pack will display the appropriate yellow and red clearance in accordance with the timing settings of the 3rd and 4th clearance intervals of the “parent” phase. Figure 11-8a and Table 11-20 show an example of a double clearance operation. Faces 3 and 4 would be on one double clearance switch pack while a separate double clearance switch pack would be used for Faces 7 and 8.
D.5 Double Clearance/Overlap Function. Any switch pack can perform the function of either of the two double clearance/overlap outputs provided by the Model 179 controller. The double clearance/overlap output combines the functions of the double clearance and the overlap output. As a result, the double clearance/overlap switch pack will display a green whenever the “parent” double clearance phase(s), and “parent” overlap phase(s), are timing a green interval. The double clearance/overlap switch pack will display the appropriate delayed double clearance whenever the “parent” phase(s) is terminating, except that it may display the green during the clearance when cycling from a phase that allows a certain traffic movement, to another phase that also allows that traffic movement. Any double clearance/overlap switch pack should be shown in the Table of Switch Packs.
D.6 Master Coordination Outputs. These outputs allow the Model 179 controller to output Cycle, Offset, Sync and Free via switch pack output. These outputs are used in association with Coordination and Interconnection, which will be discussed in Section 11.3.3.5.F.
D.7 Miscellaneous Outputs. There are two miscellaneous switch pack output functions.
D.7.a Auxiliary Output by Timeclock. The output of Switch Pack 9 yellow is capable of being controlled by time clock. Whenever the time clock indicates that the output should be active, Switch Pack 9 yellow will be turned on. Accordingly, this output could be used to control any
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device that needs to be turned on and off on a regular time clock basis. Since Switch Pack 9 can also be assigned any of the various functions available to any switch pack, care should be taken not to assign conflicting uses of Switch Pack 9 yellow when using this feature. The use of this function should be shown in the Table of Switch Packs.
D.7.b Blue Light Output. The output of Switch Pack 11 yellow is capable of being outputted during preemption operation as a blue light or any other appropriate preemption vehicle indication. If used, the output of Switch Pack 11 yellow will be turned on when the controller enters its appropriate preemption condition, and will remain on for the entire preemption timing period. The output may be programmed as a flash or steady output. Since Switch Pack 11 can also be assigned any of the various functions available to any switch pack, care should be taken NOT to assign conflicting uses of Switch Pack 11 yellow when using this feature. The use of this function should be shown in the Table of Switch Packs.
E. Assignment of Switch Packs
The NYS Model 330 Controller Cabinet is equipped with a NYS Model 215 Current Monitor. The major function provided by the Model 215 Current Monitor is to detect the condition where all bulbs are not functioning for red indications on an approach to an intersection. When this occurs the traffic control signal is placed in flashing operation. Accordingly, the current monitoring of switch packs must be taken into consideration when assigning the function of switch packs.
There are three major considerations in determining the need to current monitor a switch pack:
• The electrical operation of the switch pack. • The functional operation of the switch pack. • The need to current monitor circuit breakers feeding the switch packs.
Table 11-22, “Current Monitoring Design Chart” guides in making these decisions. The following is a discussion of the considerations used in developing Table 11-22.
Electrical operation of the switch pack: In order to current monitor a switch, the operation of the switch pack from an electrical viewpoint must be such that the switch will draw at least 0.4 amps from any one or combination of its 3 switches at all times during its normal operation. If this is not the case, then the switch pack cannot be current monitored (without using dummy loads) regardless of other factors.
Examples of switch packs that can be current monitored as a result of their electrical operation are:
• Normal green/yellow/red vehicle indications. • Full-time flashing red indications. • Pedestrian WALK/DONT WALK indications.
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Examples of switch packs that cannot be current monitored as a result of their electrical operation are:
• Left green/left yellow arrow permissive/protected left-turn phases. • Right green/right yellow overlap indications. • Preemption blue light indication.
Table 11-22 Current Monitoring Design Chart Switch Pack Current Monitoring Required for Current Monitoring Required for Output Function Switch Pack with this Function Circuit Breakers With This Function
G/Y/R Yes. Yes. SP cannot be allowed to go LGA/LYA/LRA dark if CB trips and 3-color VGA,RGA/Y/R operation continues. Decision to G/Y/Flashing R current monitor any SP with this function automatically requires CB monitoring.
Pedestrian (A) If signal layout is such that For criteria (A) CB - No. SP could WALK/DONT normal vehicle indications could be allowed to go dark if CB trips WALK serve as backup in the event of and 3-color operation continues. indications burnouts, then current Assumes trouble call will follow. monitoring is not required. For criteria (B) - Yes. SP cannot (B) If this is not the case, then be allowed to go dark if CB trips current monitor is required. and 3 - color operation continues. Decision to current monitor any SP with this function automatically requires CB monitoring.
Left-Turn Phase No. Cannot be current No. SP could be allowed to go dark with LGA and monitored. if CB trips and 3-color operation LYA continues. Assumes circular G/Y/R primary approach indications will control traffic until trouble call is responded to.
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Table 11-22 Current Monitoring Design Chart (Continued) Switch Pack Current Monitoring Required for Current Monitoring Required for Output Function Switch Pack with this Function Circuit Breakers with this Function
Overlap with RGA No. Cannot be current No. SP could be allowed to go and RYA monitored. dark if CB trips and 3-color operation continues. Assumes circular G/Y/R primary approach indications will control traffic until trouble call is responded to.
Preemption Blue No. Cannot be current No. SP could be allowed to go Light monitored. dark if CB trips and 3- color operation continues. Assumes a trouble call will follow.
Full time flashing Yes. SP must be current Yes. SP cannot be allowed to go R vehicle monitored. dark if CB trips and 3-color indications operation continues. Decision to current monitor any SP with this function automatically requires CB monitoring.
Miscellaneous Depends on function. SP can Depends on function. Can the such as auxiliary be current monitored if function SP be allowed to go dark and outputs for signs, draws greater than 0.4 amps at wait for a trouble call if the CB full-time GA all times during normal trips and 3-color operation indications, etc. operation. continues?
Key: SP = Switch Pack, CB = Circuit Breaker, G= Green, Y =Yellow, R = Red, LGA = Left Green Arrow, LYA = Left Yellow Arrow, LRA = Left Red Arrow, VGA = Vertical Green Arrow, RGA = Right Green Arrow
Functional operation of the switch pack: Once it is determined that a switch pack could be current monitored based on its electrical operation, the desirability of monitoring it based on its functional operation must be considered. This process involves assessing the relative trade-offs of placing the signal in flash due to a burn out of all indications on the switch pack, versus allowing the indications to go dark while maintaining 3-color operation at the signal.
For example, subject to approval by the Regional Traffic Engineer, at locations utilizing pedestrian indications where the signal layout is such that pedestrians could also view appropriate vehicle indications, if the pedestrian indications suffer a total burnout on a switch pack, it is preferable to leave the indications dark and maintain 3-color operation, rather than to go into flashing operation. The assumption is that the burned out pedestrian indications will eventually result in a trouble call, and pedestrians can rely on the vehicle indications as a back- up until the signal is repaired.
§11.3.3.5 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-169
Current monitoring of signal head circuit breakers: Each Model 330 cabinet with current monitor contains a set of 4 circuit breakers that feed either 2 or 4 switch packs per the following:
Circuit Breaker 1 - Switch Packs 1, 2, 13, and 14 Circuit Breaker 2 - Switch Packs 3, 4 Circuit Breaker 3 - Switch Packs 5, 6, 11, and 12 Circuit Breaker 4 - Switch Packs 7, 8, 9, and 10
The circuit breakers are manufactured with mechanical connection between the 4 units to ensure that if one breaker trips, the entire group will trip. The cabinet is, in turn, designed to sense this common trip of the 4 breakers and place the signal in flash. When the cabinet places the signal in flash mode, power is provided to the flashing signal indications through the Flash Transfer Relays. This mechanical connection of circuit breakers does not always work. The result is that a circuit breaker can trip, and all associated switch packs and signal indications go dark, while the signal continues in the 3-color mode.
To protect against this, the circuit breakers should be monitored using the capabilities of the current monitor, as the tripping of a circuit breaker will result in no current draw on all switch packs fed by that circuit breaker. This process involves determining the switch packs which are used in the signal operation, and, based upon the switch pack/circuit breaker interconnection, which circuit breakers are used. For each circuit breaker that is used in the operation, at least one switch pack fed by that circuit breaker must be current monitored, unless every switch pack fed by that circuit breaker has a function such that it is preferable to allow the signal indication to go dark rather than put the signal into the flash mode.
For example, consider a location that uses Switch Pack 11 yellow for a preemption blue light. This is fed by Circuit Breaker 3. Assume that Switch Packs 5, 6, and 12, also served by Circuit Breaker 3, are not used. At locations such as this, if the circuit breaker feeding the preemption blue light were to trip, the Regional Traffic Engineer may prefer the signal to remain in 3 color operation without blue light capability, rather than go to flash. The assumption is that the inoperative blue light will eventually result in a trouble call.
Another example is the case of the left green/left yellow arrow permissive-protected left-turn or the right green/right yellow arrow right-turn overlap. In both situations, vehicles controlled by the left-turn or overlap indications are also controlled by the primary approach faces (red, yellow, green) during appropriate parts of the signal cycle. In the event the circuit breaker feeding these indications were to trip, and the signal were to remain in the 3-color operation, these indications could be allowed to go dark, with vehicles controlled by the primary approach faces until a trouble call is responded to.
Note that in the case of the left green/left yellow arrow permissive-protected left turn, it may be desirable to monitor the circuit breaker feeding the switch pack, particularly where opposing permissive-protected left turns exist. This is because if the circuit breaker(s) feeding opposing left turns were to trip and the signal remained in 3-color operation, the signal would likely display all red to the intersection while timing the opposing left turns, which would be dark. The major function provided by the current monitor is to detect all-red bulb outs on an approach
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to an intersection. However, if the signal operation is designed such that opposite approaches to an intersection are controlled by the same phase, and thus by the same switch pack, one complete approach could burn out, and as long as one indication remained on the opposite approach, the current monitor would not trip. Consider splitting control of approaches in cases such as this by using concurrent phases so that the primary indications on each approach are serviced by a separate switch pack when feasible.
With the Model 179 controller, if splitting control of opposite approaches into concurrent phasing is not desired, it is also possible to assign 2 switch packs to the same phase function, thereby controlling opposite approaches by separate switch packs assigned to the same phase.
The following procedure should be used to determine current monitoring and switch packs assignments.
1. Based on the desired signal design, determine the switch packs (SPs) that will be used in the operation. Circle these on the 2nd row of Table 11-23.
2. Using Table 11-22, determine which switch packs must be current-monitored (2nd column). Circle these on the 3rd row of Table 11-23.
3. Using Table 11-22, and referring to the switch pack/circuit breaker association as shown in 2nd row of Table 11-23, determine which circuit breakers must be current- monitored and circle these on 1st row of Table 11-23.
4. Referring to Table 11-23 for each circuit breaker (CB) that is circled in the 1st row, at least one switch pack must be circled (current-monitored) in the 3rd row. If this is not the case, reassign switch pack outputs until this criteria is met.
5. As a check, refer to Table 11-23. If the 2nd row indicates that a switch pack is used in the signal operation, but the 1st row indicates that the corresponding circuit breaker does not require current monitoring, then the function of this switch pack must be such that it can be allowed to go dark while 3-color operation is maintained if the breaker trips.
Table 11-23 Current Monitoring Design Worksheet Circuit Breaker No.
Current 1234 Monitoring Switch Assignment
SP Fed By CB 1-2-13-14 3-4 5-6-11-12 7-8-9-10
SPs That Are 1-2-13-14 3-4 5-6-11-12 7-8-9-10 Current-Monitored
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F. Coordination and Interconnection Considerations
Coordination of traffic signal operation is a term used to describe a process in which two or more intersections are synchronized so that vehicles can pass through each intersection without stopping. Coordination is accomplished by synchronizing each coordinated phase(s) (Main Street) green of each intersection to a system reference point.
The coordination of signal operation between adjacent intersections offers an opportunity for significant benefits to motorists. On open highways, traffic flow is characterized as being random in that it is not normally influenced by upstream interruptions. Its arrival at a point is generally uniform throughout a selected time interval. In contrast, traffic flow on urban streets is generally less uniform because of interruptions, and it tends to flow in pulsed groups of vehicles, or platoons. Signal coordination simply attempts to recognize this flow characteristic and coordinate signal operation to accommodate platoons with minimal stops. The success of signal coordination is influenced by the following factors:
• Signal spacing. • Signal timing (cycle length and split). • Traffic volumes. • Amount of turning traffic. • Midblock storage or contributions of traffic.
Safety and driver comfort (satisfaction) should also be appraised when considering signal coordination. Safety can be enhanced through progressive movement along thoroughfares where stops and delays are reduced. Driver comfort and satisfaction are influenced by the expectation of “system” operation where traffic moves smoothly with few stops, and trip times are generally repeatable along the same route. In fact, the layperson’s view of good signal timing is where progression permits continuous movement, and they are able to observe route continuity and consistency but not optimized system-wide measures of effectiveness.
There are two ways to interconnect traffic signals, direct and indirect. Direct means use a physical connection between controller assemblies; indirect means rely on an air path or time- based approach.
Direct connection uses one of several types of connections and cables, as follows:
1. Electrical Cables (Wires): The most widely used cable consists of a minimum of 7- conductor (AWG 14) cable physically linking each controller. In a Model 179 traffic signal controller, this cable would be connected from a switch pack output at one controller to an input of the next controller. The switch pack output would be programmed for the required Master Coordination Output (free, offset, synch, or cycle) while the input at the second controller would be programmed for the same function. The second controller would use a Model 252, dual A.C. isolation module in the detector input rack.
2. Data Communication Cable: Sophisticated systems use digital data communication techniques rather than energized circuits, and the direct wire cables contain data communication twisted wire pairs. These systems use modems at both ends to encode
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and decode (multiplex) the data. Model 179 controller systems using the Model 400 modem require a 4-pair, 18-gauge shielded communications cable which will be connected to the C2 connector on the Model 179.
3. Coaxial Cable: Coaxial cable has a large signal information capacity and has come into widespread use for cable TV systems. Its “broadband” characteristics make it well suited for the transmission of video signals within narrow slices, or channels, of its bandwidth. Again, modems are required at both ends to multiplex the data. This type of cable may be used on large Intelligent Transportation System (ITS) type systems.
4. Fiber Optic Cable: Developments in the use of fiber optics for communication have made this medium attractive for use in computerized traffic systems. Fiberoptic cable size is much smaller than wire cable and often can be included in existing conduit. Modems convert multiplexed data into light pulses rather than electrical pulses.
Indirect connection uses one of the following methods:
1. Radio Communications: Radio represents an indirect method of interconnection that is not widely used, but can be effective in certain situations. As generally used, it is a one-way form of data communication from a central transmitter to multiple receivers at intersection controller assemblies.
2. Time-based Coordinators (TBC): One of the most popular advances in signal coordination has been the time-based coordinator. Working without cables, this device functions as a very accurate clock to supervise a controller unit locally by the transmission of sync pulses and commands, much like a system master unit. Adjacent traffic signals operate from the same reference point, providing a high level of coordination. The primary disadvantage is that two-way communication is not achieved. The Model 179 controller comes programmed with time based coordination capability.
The designer should confer with the Regional Traffic Engineer concerning the need for, and type of, coordination and interconnection to be used.
11.3.3.6 Electrical Service and Equipment Wiring
A. Power Cable
The requirement for connecting electrical power from the local utility lines to signal equipment may vary among electrical power companies. Service connections normally consist of a single- phase circuit of 110 volts to 120 volts, 60 Hz, connected to the nearest source of power. The service point may be from either an overhead or underground power line. The service cable must be connected to an electrical meter if required by the utility company and must always be connected through a disconnect box as shown on Standard Sheet “BASE - AND POLE - MOUNTED CABINET INSTALLATION DETAILS”. The most important aspects of the service connection are that the connection point is located as close as possible to the controller cabinet
§11.3.3.6 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-173
and the wire is of adequate size and capability to minimize voltage drop to less than 5% of the utility voltage. Locating the controller close to the power source is generally a trade-off between the length of the service cable and the lengths of the signal control wiring. The controller cabinet should also be located to be readily accessible to maintenance/service personnel and preferably be on the same side of the road as any interconnection cable. Two #6 or #8 AWG single conductor cables should be used for the service connection. Typical service connections are shown on Standard Sheets “SPAN WIRE MOUNTED TRAFFIC SIGNAL INSTALLATION DETAILS” and “BASE - AND POLE - MOUNTED CABINET INSTALLATION DETAILS”.
B. Signal Cable
Signal head wiring originates at the terminal block in the controller cabinet and terminates at the signal head. Number 14 AWG conductors are generally used for signal head wiring. The number of conductors making up the cable is a function of the signal operation and head layout. The number of conductors and suggested color code is shown in Section 680 of the Standard Specifications. Each signal lamp requires one conductor plus a common. Some spare conductors should be provided in each signal cable.
Generally, either 2-, 10-, 15-, or 19-conductor cable is used for signal head wiring. Two-phase signal operation requires 10-conductor cable. Three-phase operation with no overlaps requires 15-conductor cable. Three-phase operation with one overlap requires one 19-conductor cable while 4-phase through 8-phase operation may require from 1 to 3 cables of the appropriate number of conductors. Five conductor cable is generally used for pedestrian signal head wiring. The number of conductors and color code shown in the Standard Specifications works well for signal installations with 1 span wire assembly. If 2 span wire assemblies or mast arm installations are used, several signal cables may be required. In such cases, determine the number of conductors needed in each cable (2 for each lamp plus a minimum of 2 spares) and then select the next larger cable size from the standard sizes used (10-, 15-, or 19- conductor). The signal head wiring for each signal installation should be shown in the Table of Switch Packs. There is great variation among Regions in how to show the wiring and electrical requirements. Procedures may range from simply listing the required cable to a detailed wiring diagram which shows the individual conductors, their color code, and their terminal position. A wiring diagram should identify the number of conductors in each conduit between the controller cabinet and the signal head assembly, and the detectors. Examples of various ways of showing wiring information can be found in the Institute of Transportation Engineers’ Manual of Traffic Signal Design.
C. Inductance Loop Wire
The inductance loop wire is a 1-conductor #14 AWG wire loosely encased in a tube and embedded in a saw-cut slot in the pavement to form a loop configuration. See Section 11.3.2 for additional information on the design and operation of loop detectors. Section 680 of the Standard Specifications and Standard Sheet “INDUCTANCE LOOP VEHICLE DETECTOR INSTALLATION DETAILS” detail the installation of inductance loop detectors.
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D. Shielded Lead-In Cable
The shielded lead-in cable is the electrical cable used to connect the inductance loop wire to the input of the loop detector unit in the controller cabinet. This cable is sometimes called the “home-run” cable or transmission cable. The shielding is provided by a conductive material surrounding the pair of lead-in wires, so that outside electrical interference will not induce noise onto them.
E. Shielded Communication Cable
The shielded communication cable is the cable used to interconnect traffic signals to provide coordinated operation. In general, the cable types used for interconnecting controllers are twisted, shielded pairs of conductors in cables ranging from two pairs to hundreds of pairs. The functions of the twisting and shielding are similar in that both reduce interference (crosstalk) which might distort the message on the communication channel.
To interconnect Model 179 controllers using Master/Slave TAPS communication software, the shielded communication cable should consist of 4 pairs of #18 AWG wire. This cable would not be used to interconnect signals using the output of a switch pack to the input of an A.C. isolation module. Standard #14 AWG signal cable should be used for this type of interconnect. Shielded communication cable should not be placed in close proximity to power cables or signal cables due to noise induced by those cables. The designer should also advocate the use of surge protection for the cable to insure that transients, caused by high power surges such as lightning, do not flow through the system.
F. Conduit
Underground cable should normally be housed inside conduit. Only detector sensor cable and direct burial cable should be installed without conduit. Conduit offers some measure of protection for conductors from physical damage and moisture. Direct burial cable can eliminate the need for some conduit and possibly some pullboxes, however, a trench must be excavated to remove or replace damaged cable. Wiring housed in conduit can be removed or added from a pullbox without the necessity of digging a trench.
Steel conduit may be installed in a trench, pushed underground, or attached to a pole. It is normally used due to its structural strength and its availability as a grounding system.
Polyvinyl chloride (PVC) and other plastic conduit should only be installed in a trench or attached to a structure. PVC conduit should not be used under load bearing surfaces, such as roads or driveways, except in a magnetic detector installation. Steel conduit used with a magnetic detector probe could result in a constant call. A #6 AWG ground wire should be installed in all nonmetallic conduit and should be grounded at both ends.
The size of the conduit is determined by the number and dimension of the cable(s) to be housed
§11.3.3.6 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-175
within the conduit. The cross sectional area of the cables is totaled and a conduit large enough to easily accommodate these cables is selected. Conduit shall be large enough to meet the requirements (31% full for 2 conductors, 40% for 3 conductors) in Chapter 9 of the National Electric Code (NEC). It is considered good practice to provide extra space for future additional cable and for ease in pulling the cable through. Bends in the conduit should be kept to a minimum to facilitate pulling the cable. Avoid more than three 90° bends in cable runs of 30.5 m or less. If future need for additional conduit under the roadway is anticipated, the installation of the added conduit during the original installation will save time, effort, and the expense of digging up the road to lay conduit a second time. Extra conduit should also be installed in controller cabinet base foundations and signal pole foundations if the need for additional wiring at a later date is anticipated.
G. Pullboxes/Junction Boxes
Pullboxes are used near a cabinet or pole as a junction point for incoming and outgoing conduit, near detector locations to house the splice between sensor cable and shielded lead-in, and as a pulling station on long conduit runs. Pullboxes should be located in back of the edge of shoulder or curb line where they will not interfere with pedestrian or vehicular traffic. The pullbox size will be dependent on the number and size of entering/leaving conduits or cables and what work is required within the box. Extra pullboxes should be considered at all locations where conduit changes direction. For long conduit runs pullboxes should not be placed more than 60 m apart.
H. Grounding
Traffic signal poles and controller cabinets shall be electrically grounded in accordance with the Standard Sheets, Standard Specifications, National Electrical Code, and Traffic Engineering and Highway Safety Division’s Signal Installation Manual.
I. Utility Clearances
The required offset distance between traffic signal equipment and existing overhead and underground utility lines varies among different utility companies and should be determined by contacting each individual utility involved. The clearance distance must meet or exceed the requirement of the National Electrical Safety Code (NESC) ANSI C2, 1997, published by IEEE. If the clearance required by any utility company is less than the NESC standard, the NESC standard shall apply.
J. Wood Poles
Wood poles may occasionally be used in signal installations. They are most often used in temporary signals and to carry overhead wires in interconnected signal systems. Wood poles at each end and at each change of direction along the run of interconnect cable should be guyed
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as shown on the Standard Sheets. If a cabinet is mounted on a wood pole it shall be grounded by a #6 copper ground wire and a copperweld ground rod in accordance with the Standard Specifications and Standard Sheets. A wooden pole requires that wiring be run up the outside of the pole. Wiring must be housed in a conduit riser installation, details of which are shown in the Standard Sheets.
11.3.3.7 Model 170/179 Microcomputer Traffic Signal Controllers
The Model 170 controller is a microcomputer (Motorola MC6800 MPU) based unit jointly developed by the states of New York and California. Since its introduction, many states and other traffic organizations have adopted the Model 170 controller. The controller unit contains a microcomputer which, with the addition of appropriate software, can provide a variety of control applications. New York State’s Isolated Traffic Actuated Processing (ITAP) software is used with the Model 170 to provide traffic signal control in New York State.
In 1985 New York State upgraded the Model 170 specifications to use a Motorola MC6809 microprocessor unit. The new traffic signal controller unit is known as the Model 179. The specifications for the Model 179 controller, Model 330 pole-mounted controller cabinets, and associated peripheral equipment can be found in Traffic Engineering and Highway Safety Division’s New York State Transportation Management Specifications. It should be noted that the Model 330 pole-mounted controller cabinet may also be mounted on a concrete base. See Standard Sheet “BASE - AND POLE-MOUNTED CABINET INSTALLATION DETAILS” for details on ground mounting the Model 330 cabinet. All traffic signal operations for traffic signals to be maintained by NYS DOT should be designed to use the Model 179 controller.
As with the Model 170 controller, the Model 179 with appropriate software can provide a variety of control applications. As of this time, the Traffic Engineering and Highway Safety Division provides software for the following applications:
• Traffic Signal Controller - Traffic Actuated Processing System (TAPS). • Time-Base Coordination - Traffic Actuated Processing System (TAPS). • Closed-Loop System - Developed by Bi Tran Systems Inc. (Statewide License). • Ramp Metering - Model 179 Ramp Metering Software Program (GATER).
Operator’s manuals for these software systems can be obtained from the Traffic Engineering and Highway Safety Division.
The TAPS program is designed to perform the functions of a typical 2-phase through 8-phase traffic signal controller, using either a standard dual ring, or a 6-phase sequential format. Each of the 8 vehicular phases is capable of density timing, as well as concurrent pedestrian timing, 3 maximum greens selected by time of day, all red clearance timing, and double clearance timing. A variety of vehicle- and pedestrian-actuated, and recall green modes are also available for actuated and fixed- time operation.
The program provides the capability of outputting up to 14 switch packs for traffic signal indications. All switch packs are fully user programmable, and can be implemented in any combination of the
§11.3.3.7 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-177 following:
• Up to 8 vehicular and pedestrian phases. • Up to 6 overlaps. • Up to 6 pedestrian movements. • Up to 6 double clearances. • Up to 2 overlaps of double clearances. • Special outputs including a blue light for emergency vehicle indication, and an output that is controlled by a time clock.
Other major software capabilities of the program include:
• Programmable start-up sequence and phases. • Up to 28 inputs, each of which is programmable by function, and capable of extensions and delays. • Capability to flash any outputs during 3-color operation. • Light reduction. • Up to 4 phase omits for priority servicing of selected phases. • 3 emergency preemptions, including one railroad preempt. • A 52-week clock with built-in daylight savings time and leap year adjustments. • A time clock capable of implementing up to 192 day program events, 10 week programs, 26 yearly week program changes and 16 exception days. • 8 time clock functions capable of being implemented at any day program event. These functions include 2 phase omits, rest-In-red, auxiliary output, 2 max greens, input by time clock, and flashing operation. • Detector failure analysis with built-in corrective action. • Exclusive pedestrian phase. • Time-based coordination.
This program can be used for almost all 2-phase through 8-phase fixed time or actuated signal operations. For additional information on the capabilities and flexibility of TAPS see Section 11.3.4 Signal Operation Design and the TAPS Operator’s Manual.
11.3.3.8 Administrative Issues
The Model 179 controller, Model 330 Pole-Mounted Controller Cabinet and associated peripheral equipment are supplied to construction contracts by the Department from its inventory. For all projects where there is State-supplied traffic signal equipment, 1 copy of Form TE 200c “Traffic Signal Equipment Furnished by New York State Department of Transportation” must be completed for each signal location and included in the PS&E submittal.
The following procedure must be used to ensure that the equipment is actually installed and to obtain reimbursement for the cost of the equipment.
1. The Regional Design Group will submit 1 Form TE 200c for each traffic signal with the PS&E submittal to the Design Quality Assurance Bureau (DQAB) with the Engineering
3/15/02 §11.3.3.8 11-178 SIGNS, SIGNALS, AND DELINEATION
Share Box, Description, PIN, and Estimated Quantity Boxes filled in. Do not fill in the unit price or estimated amount columns.
2. DQAB will complete the Contract Number and forward the form to the Traffic Engineering and Highway Safety Division, Traffic Operations Bureau.
3. The Traffic Operations Bureau will complete the unit price and estimated amount columns and return the form to DQAB.
4. DQAB will complete the expenditure codes, Federal-Aid Project Number, and Fiscal Share Number boxes, and transmit the form to the Accounting and Fiscal Services Bureau with a copy of the form to the Construction Division.
5. The Appropriation Control Unit of the Accounting and Fiscal Services Bureau will prepare an accounting entry to charge the cost of the State-furnished signal equipment against the project involved.
6. The Construction Division will transmit the form to the Regional Construction Group at the time the contract is awarded.
7. The Regional Construction Group will forward the form to the Engineer-in-Charge.
8. When the final quantities of the traffic signal equipment to be furnished by the Department are known, the Engineer-in-Charge enters the final quantities on Form TE 200c, signs the form, and forwards it with the Final Agreement through the Regional Office to the Construction Division.
9. The Construction Division will forward the form to the Traffic Engineering and Highway Safety Division, Traffic Operations Bureau who in turn will advise the Accounting and Fiscal Services Bureau of any changes.
10. The Appropriation Control Unit of the Accounting and Fiscal Services Bureau will prepare an accounting entry to adjust the cost charged to the project to the actual cost based on the report of the State-furnished signal equipment actually installed in the project.
For traffic signal equipment which will be maintained by an agency other than NYSDOT, the designer must work with that agency to provide equipment which they are capable of maintaining.
§11.3.3.8 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-179
11.3.4 Plans and Specifications
Accurate and complete plans and specifications are a necessary part of the contract documents to help reduce change orders and potential disputes which may occur during construction.
11.3.4.1 Traffic Signal Plans
The traffic signal plans and details should provide the information necessary for a contractor to bid and construct the traffic control signal. Guidance regarding traffic signal plans is provided in Chapter 21, Section 21.2.2.17 of this manual, and additional guidance is provided in Section 11.3.4.2 to facilitate the development of the traffic signal plans.
11.3.4.2 Signalization Details
Either on the traffic signal plan or on a separate sheet, specify the details associated with each installation. The tables required in Chapter 21, Section 21.2.2.17 of this manual and discussed in the following sections should be prepared using the working tables provided in the nytraffic.cel cell library.
A. Table of Quantities
The item number, description, work unit and estimated quantities of materials and equipment for each signal installation or modification should be listed separately and totaled as a summary for the project. Materials and equipment that will be provided by NYS DOT to the contractor must be clearly identified (e.g., Model 179, poles, signal heads) or listed separately from those items to be supplied by the Contractor. Figure 11-11 shows a Table of Quantities. See Section 11.3.3.8 with regard to the need for a form TE 200c for State-supplied equipment. (See Chapter 21 of this manual for additional details.)
Figure 11-11 Table of Quantities TABLE OF QUANTITIES
ITEM ESTIMATED FINAL NUMBER DESCRIPTION UNIT QUANTITY QUANTITY
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B. Table of Operation (Table of Sequence)
A Table of Operations is required for each proposed signal installation. The Table of Operations should define each signal face configuration, the vehicular and pedestrian phases utilized by the controller to be installed, the respective signal indications for each signal face during a particular phase or combination of phases, the startup indication/startup phasing, and the emergency flashing operation for the intersection. A Table of Operations is shown in Figure 11-12.
Figure 11-12 Table Of Operations TABLE OF OPERATIONS
FACE PHASE 12345678910111213141516
Startup
FLASHING OPERATION
DISPLAY
300 mm DIAMETER LENSES 1
1. In this example all lenses are 300 mm. Lenses should be specified consistent with the NYS MUTCD Section 272.10.
§11.3.4.2 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-181
C. Table of Clearances
The Table of Clearances should be prepared to define the appropriate signal indications displayed during each clearance interval. Clearances are necessary between signal indications which convey different messages to motorists. Generally, clearances are composed of two parts; a yellow indication and an “all-red” time period before the green is given to an opposing movement (the all-red time period may be omitted if it is not needed). The yellow indication advises traffic that the related green period on the approach is being terminated and a red indication will be displayed immediately thereafter. The all-red time period is used to provide additional time for a vehicle to clear the intersection. These clearance indications may also be shown in the Table of Operation. A table of clearances is shown in Figure 11-13.
Figure 11-13 Table of Clearances
TABLE OF CLEARANCES
FROM TO
D. Table of Switch Packs
The Table of Switch Packs should be prepared to show the wiring of each section of the traffic signal head to the output terminal board in the traffic signal controller cabinet. The first column should provide the switch pack number, from 1 to 14. The second column should indicate the function that each switch pack will be used for (output functions are discussed in Section 11.3.3.5.D). The third column entitled Face Numbers should show the face number (from the traffic signal plan) that will be connected to the subject switch pack. The Flash Plug Color column should be used to indicate which switch packs will flash red or yellow during emergency flashing operation. The indication (red, yellow, walk, etc.) connected to each switch pack output should be shown in the Indication column. The color code for each conductor connect from the switch pack output terminal to the signal indication should be shown in the Wire Color Code column. Some Regional Traffic Groups may choose to have the signal heads wired to the terminal board by the Regional Traffic Signal Crew in which case the Table of Switch Packs may not be required in the Contract Plans. A Table of Switch Packs is shown in Figure 11-14.
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Figure 11-14 Table of Switch Packs TABLE OF SWITCH PACKS
Signal No.______County :______
FLASH TERMINAL WIRING BOARD SWITCH FACE PLUG PACK FUNCTION NO.S COLOR INDICATIONS TERMINAL WIRE COLOR CODE
SP 1R SP 1 SP 1Y SP 1G GRND WIRE GRND BUS
SP 2R SP 2 SP 2Y SP 2G GRND WIRE GRND BUS
SP 3R SP 3 SP 3Y SP 3G GRND WIRE GRND BUS
SP 13R SP 13 SP 13Y SP 13G GRND WIRE GRND BUS
SP 14R SP 14 SP 14Y SP 14G GRND WIRE GRND BUS
E. Table of Input Wiring
The Table of input wiring should be prepared to show how each detector, pedestrian pushbutton, etc. is connected to the input terminal board in the traffic signal controller cabinet. The first column is entitled “Function” and is used to indicate the signal phase or preemption the input device calls. Input functions are discussed in Section 11.3.3.5.C. The second column entitled “Detector Number” is the detector number from the plan sheet for the signal. The column entitled “Type” should indicate what type of device (e.g., loop detector, calling detector, pushbutton, presence detector, etc.) is connected to the input (See Section 11.3.3.5).
Each input slot in the input rack controls an odd and even input number (e.g., 1 & 2, 3 & 4) and does not mix detector types. Also, when using the microwave detectors with type TCPS-1 power supply/ iso modules, the input will be on the odd-numbered terminal and the 12 V AC power supply to the unit will be on the even-numbered terminal.
§11.3.4.2 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-183
Figure 11-15 Table of Input Wiring TABLE OF INPUT WIRING
DETECTOR TERMINAL FUNCTION NUMBER TYPE BOARD WIRING REMARKS
1A, 1B
2A, 2B
3A, 3B
4A, 4B
F. Table of Magnetic Detectors
The Table of Magnetic Detectors should be prepared to show each magnetic detector to be installed. “Detector Number” is the detector number from the plan sheet for the signal. The phase number is the traffic control signal phase that will be called by the detector. The number of magnetic probes represented by each detector number is shown in the “Magnetic Detector Probes” column. The length of 3 NPS PVC conduit for each detector is shown in the next column. The number of dual magnetic amplifier units is shown in the last column. Note that 2 magnetic detectors can be attached to each amplifier unit. Figure 11-16 shows a Table of Magnetic Detectors.
Figure 11-16 Table of Magnetic Detectors TABLE OF MAGNETIC DETECTORS
DETECTOR PHASE MAGNETIC DETECTOR 3 NPS PVC DUAL MAGNETIC NUMBER NUMBER PROBES CONDUIT AMPLIFIER UNITS
G. Table of Magnetometer Detectors
The Table of Magnetometer Detectors should be prepared to show each magnetometer detector to be installed. “Detector Number” is the detector number from the plan sheet for the signal. The “Phase Number” is the traffic control signal phase that will be called by the detector. The “Magnetometer Channel No.” column is used to indicate the channel of the detector amplifier the probes are to be connected to. The number of magnetometer probes connected to each detector is shown in the “Number of Probes” column. The spacing between each probe is shown in the “Spacing” column. The number of dual magnetometer amplifier units is shown in the last column. Note that 2 magnetometer detectors can be attached to each amplifier unit. One dual magnetometer amplifier unit uses 4 input positions on the input terminal board. Figure 11-17 shows a Table of Magnetometer Detectors.
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Figure 11-17 Table of Magnetometer Detectors TABLE OF MAGNETOMETER DETECTORS
NUMBER DUAL CHANNEL DETECTOR PHASE MAGNETOMETER OF SPACING MAGNETOMETER NUMBER NUMBER CHANNEL NO. PROBES DETECTORS
H. Table of Microwave Detectors
The Table of Microwave Detectors should be prepared to show each microwave detector to be installed. “Detector Number” is the detector number from the plan sheet for the signal. The “Phase Number” is the traffic control signal phase that will be called by the detector. The number of microwave detector units is shown in the “Microwave Detector Units” column. The type of mounting (band on pole, mast arm mount, etc.) is shown in the “Type of Mounting” column. Microwave detector units are interfaced to the Model 170/179 controller using an isolation module. The number of isolation modules is shown in the last column. Figure 11-18 shows a Table of Microwave Detectors.
Figure 11-18 Table of Microwave Detectors
TABLE OF MICROWAVE DETECTORS
DETECTOR PHASE MICROWAVE TYPE OF TCPS-1 SINGLE NUMBER NUMBER DETECTOR UNITS MOUNTING ISOLATION MODULES
I. Table of Inductance Loop Design
The Table of Inductance Loop Design should be prepared to show each inductance loop to be installed. “Detector Number” is the detector number from the plan sheet for the signal. The phase number is the traffic control signal phase that will be called by the detector. The width and length of the loop should be shown in the “Inductance Loop Size” column. The width of the loop is generally 1.8 m to ensure that there are no dead spots and that an adequate detection area is provided. The “Number of Turns” column is used to show how many turns of loop wire are required for the loop. The “Jct Boxes” column shows how many junction boxes are required at each loop. The length of 1¼ NPS conduit required for each loop is shown in the “1¼ NPS
§11.3.4.2 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-185
Conduit” column. The number of dual loop detector amplifier units is shown in the last column. Note that 2 loop detectors can be attached to each amplifier unit. Figure 11-19 shows a Table of Inductance Loop Design.
Figure 11-19 Table of Inductance Loop Design
TABLE OF INDUCTANCE LOOP DESIGN
DETECTOR PHASE INDUCTANCE NUMBER JCT 1¼ NPS DUAL LOOP NUMBER NUMBER LOOP SIZE OF BOXES CONDUIT DET. MODULES TURNS
11.3.4.3 Specifications
Designers should use either the Department's standard specifications found in Section 680 of the "Standard Specifications", or, when these specifications do not satisfy the designer's needs, write or use previously written special specifications.
Specification pay items with corresponding quantities, or notes referring to separate agreements with utilities or municipalities regarding payment for work to be performed by them, shall be provided for all aspects of the work to be performed by the contractor.
Refer to Chapter 21, Section 21.3 of this manual for further guidance regarding specifications.
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11.3.5 Terminology
The following definitions are applicable to traffic signals.
Actuated Controller. A controller for supervising the operation of traffic control signals in accordance with the varying demands of traffic as registered with the controller by traffic detectors.
Actuation. The action of a vehicle or pedestrian which causes a detector to call a specific signal phase.
Allowable Gap. The maximum time interval between successive vehicles crossing a detector which will extend the phase serving those vehicles.
Amplifier (Detector Electronics). A device that is capable of intensifying the electrical energy produced by a sensor. A loop detector unit is commonly called a detector amplifier, although its electronic function actually is different.
Arterial Intersection Control (Open Network Control). A form of control for signalized intersections along an arterial street where progressive traffic flow along the arterial is promoted.
Arterial System. A linear sequence of signals on an arterial supervised to provide progressive flow in one or both travel directions.
Audible Pedestrian Signals. An audible signal that indicates walk intervals for pedestrians.
Background Cycle. The term used to identify the cycle length established by a coordination unit and master control in coordinated systems.
Bus Detector (Passive). A pavement-installed loop detector with digital device that identifies buses.
Bus Priority. The cycle-by-cycle timing of a traffic signal so the beginning and end times of green may be shifted to minimize delay to approaching buses. The normal sequence of signal displays is usually maintained.
Cable. A group of separately insulated wires wrapped together.
Call. A registration of demand for right of way by vehicle or pedestrian traffic. The call to the controller is usually via detector actuation.
Calling Detector. A detector normally placed just upstream of the stop line to detect vehicles entering the roadway from a nearby driveway between the stop line and extension detector during a red or yellow interval. When the signal is green, the detector is ignored so that extensions of the green can come only from the detector located upstream of the driveway. A calling detector can place a maximum of one call for a phase each cycle.
§11.3.5 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-187
Check-In Detector. A vehicle presence detector placed on the approach to a ramp metering signal so that the signal changes to green only at vehicle presence.
Check-out Detector. A vehicle detector located to sense the departure of a vehicle past a ramp metering signal. Terminates the green signal after one vehicle has passed.
Clearance Interval. The interval from the end of the of the green or pedestrian walk indication of one phase to the beginning of a conflicting phase.
Closed Grid Signal System. A network of traffic control signals forming an interlocking pattern and supervised to give progressive flow in all traveled directions within the network.
Closed-Loop Control System. A traffic control system capable of controlling some operation by implementing certain strategies, receiving inputs that permit the rapid evaluation of the effects of the control, and then taking some action that modifies the strategy on the basis of the evaluation, all without the need of operator input.
Closed-Loop Signal System. A system that provides two-way communication between the intersection signal controller and its master controller. This system also provides two-way communications between the master controller and the traffic operations center.
Coaxial Cable (Coax). A transmission line in which one conductor completely surrounds the other, the two being coaxial and separated by a continuous solid dielectric or by dielectric spacers. Such a line has no external field and is not susceptible to external fields from other sources. This broad band communications technology has the capability of carrying many channels to transmit either data or video.
Concurrent Timing. Mode of operation where a traffic phase can be selected and timed independently and simultaneously with another nonconflicting traffic phase.
Conflicting Phases. Two or more phases which will cause interfering traffic movements if operated concurrently.
Controller Assembly. A complete electrical mechanism mounted in a cabinet for controlling the operation of a traffic control signal.
Controller Unit. The part of the controller assembly which performs the basic timing and logic functions.
Coordination. The establishment of a timing relationship between signal indication displays at two or more signalized locations.
Crosstalk. The mutual coupling of magnetic fields, producing interaction between two or more detector units in the same cabinet, when the units are operating at similar frequencies. Crosstalk results in a detector outputting an actuation in the absence of a vehicle (false call).
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Cycle. A complete sequence of signal phasing in a pretimed signal operation. For an actuated signal operation, a cycle is variable depending on the presence of calls.
Cycle Length. The time (in seconds) required for one complete sequence of signal phases.
Demand. The need for service, e.g., the number of vehicles desiring use of a given segment of roadway during a specified unit of time.
Demand Control (Loop Occupancy Control). A detector/controller design using long detection loops with the controller unit operated in the nonlocking mode (memory off). The call is active only when an object is present within the loop.
Detection Zone. That area of the roadway within which a vehicle will be detected by a vehicle detector.
Detector. A device for indicating the presence or passage of vehicles or pedestrians. This general term is usually supplemented with a modifier indicating type, i.e., loop detector, magnetic detector.
Detector Memory. The retention of an actuation, after a vehicle has passed the detector, for future use by the controller assembly.
Detector Setback. The longitudinal distance between stop line and detector.
Detector System. The complete sensing and indicating group consisting of the detector unit (amplifier), transmission lines (lead-in cable), and sensor.
Detector Unit (Amplifier). The portion of a detector system, other than the sensor and the lead-in, consisting of an electronics assembly which interfaces with the controller.
Dilemma Zone. A distance or time interval related to the onset of the yellow interval. Originally the term was used to describe that portion of the roadway in advance of the intersection within which a driver can neither stop prior to the stop line nor clear the intersection before conflicting traffic is released. That usage pertained to insufficient length of timing of the yellow and/or red clearance interval. More recently the term has also been used to describe that portion of the roadway in advance of the intersection within which a driver is indecisive regarding stopping prior to the stop line or clearing (proceeding into or through the intersection), although the signal timing is long enough to permit either. It may also be expressed as the increment of time corresponding to the dilemma zone distance.
Dilemma Zone Protection. Any method of attempting to control the end of the green interval so that no vehicle will be in the dilemma zone when the signal turns yellow, or delay the onset of an opposing green indication if a vehicle is in the dilemma zone.
Direct Wire. A communications method that uses wire interconnect between the transmission and reception points with no multiplexing.
§11.3.5 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-189
Directional Detector. A detector capable of being actuated only by vehicles traveling in one direction.
Distributed System. A control system in which individual computers are installed in each of the major control areas of a total system, and a supervising master is used to provide interface between the individual areas and to make decisions on timing patterns affecting two or more areas.
Downstream. The roadway extending from a reference point in the direction of the traffic movement that is being discussed.
Dual Entry. A fully activated operating mode in a dual-ring controller unit in which one phase in each ring must be in service.
Dual-Ring Controller. A controller unit that contains two interlocked rings arranged to time in a preferred sequence and allows concurrent timing of compatible phases in both rings.
Electromagnetic Field. A field produced by magnetic material surrounded by a coil of wire through which an electrical current is passed to magnetize the material.
Emergency Vehicle Preemption. The transfer of the normal control of signal to a special signal control mode for emergency vehicles.
Entrance Ramp Control. The regulation of the number of vehicles per unit of time entering a freeway so that demand on the freeway does not exceed capacity; and/or the guidance of vehicles entering a freeway into gaps in the freeway traffic stream, in order to improve the safety and capacity of the merging operation.
Extended Call. It holds or stretches the call of a vehicle for a period of time set on an adjustable timer incorporated into the detector or controller. It can be designed to begin the timing of that period when the vehicle enters the detection area, or when it leaves. This function is provided in the software in traffic signal controllers, and therefore it does not need to be provided by the detector unit.
Extension. The time interval during the extensible portion of the green which is reset by each detector actuation on the phase currently timing.
Fixed Time Operation. The preset phase green time. It is always serviced with a fixed green duration.
Flashing Beacon. A flashing beacon consists of two or more flashing yellow indications, facing in one direction, to emphasize a sign message or to warn approaching traffic of a potential hazard.
Full-Traffic-Actuated Controller Assembly. A type of traffic-actuated controller assembly in which means are provided for traffic actuation on all approaches to an intersection. Both the Model 170 and Model 179 controllers provide full-traffic-actuated operation.
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Gap. The time or distance between successive vehicles passing an individual detector.
Gap-Out. The termination of a green interval due to exceeding a selected maximum time interval (gap) between the actuations of vehicles arriving on the green, so as to service a conflicting phase.
Gap Reduction. A feature whereby the allowed time spacing between successive vehicles on the phase displaying the green during the extensible portion is reduced, so as to service a conflicting phase.
Indication. A lighted shape, word, or symbol used to control traffic.
Inductive Loop Detector. A vehicle detector system that senses a decrease in inductance of its sensor loop(s) during the passage or presence of a vehicle in the zone of detection of the sensor loop(s).
Initial Vehicle Interval. The time assigned by an actuated controller assembly to initiate traffic movement on a given phase. The length of this interval is usually set to permit clearance of vehicles stored between the detectors and the stop line on a given approach (see Variable Initial).
Interconnected Signal System. A number of intersections which are connected by wire, radio, or some other means to effect traffic progression.
Interval. The part or parts of the signal cycle during which signal indications do not change.
Lane Use Signals. The special overhead signals having indications to permit or prohibit the use of specific lanes or warn of impending prohibition. Reversible lane control is the most common use of lane control signals.
Lead-In Cable. The cable which serves to connect a detector to the detector unit in the controller cabinet (sometimes called a Home-Run Cable or Transmission Line).
Lead-In Wire. The wire between the sensor and the pull box.
Locking Detection Memory. A traffic signal controller feature, selectable for a phase, whereby the call of a vehicle passing through the detection area during the red or yellow indication for the phase is remembered, or held, by the controller until served by a green interval for the phase.
Loop detector. see Inductive Loop Detector
Loop Detector Unit. An electronic device which is capable of energizing the sensor loop(s), monitoring the sensor(s) inductance and responding to a predetermined decrease in inductance with an output to the controller which indicates the passage or presence of vehicles in the zone of detection.
Loop Occupancy Control. A detector/controller unit design using long detection loop(s) and a controller unit operated in the nonlocking mode.
§11.3.5 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-191
Magnetic Detector. A pavement installed device of coiled wire with a highly permeable core. Vehicle induced flux changes cause an induced voltage pulse. Not to be confused with a magnetometer detector. See Section 11.3.3.2.A for more information.
Magnetometer Detector. A pavement-installed device that detects change in the vertical component of the earth's magnetic field caused by the presence of a vehicle. It is not to be confused with a magnetic detector. See Section 11.3.3.2.B for more information.
Master Controller. The controller which supervises a system of coordinated signals, maintaining time relationships, and accomplishing other supervisory functions, such as turning the system on and off, placing the system in flashing operation, etc.
Maximum Gap. The selected maximum length of a gap between approaching vehicles that may hold a phase in green in the presence of an opposing call. This applies to actuated signals only.
Maximum Green. The longest time for which a green indication will be displayed in the presence of a call on an opposing phase. This applies to actuated signals only.
Merge Detector. A detector used to sense the presence of vehicles in the primary merging area of the ramp and freeway mainline.
Minimum Gap. This controller setting defines the minimum allowable gap when using the gap reduction feature (see Maximum Gap and Gap Reduction).
Minimum Green. The shortest green time of a phase.
Minimum Recall Green. The phase memory/recall position which results in the phase being served for the minimum green period equivalent to a single vehicle actuation. Additional vehicle actuation will extend the green period beyond the minimum.
Model 170 Controller. This is New York State's first microprocessor (Motorola 6800) based traffic signal controller. The specifications for this controller were jointly developed by New York and California. The traffic signal software used in New York State was developed by the NYSDOT Traffic Engineering and Highway Safety Division.
Model 179 Controller. This is New York State's microprocessor (Motorola MC 6809) based traffic signal controller. Both the specifications for this controller and the traffic signal software were developed by the Traffic Engineering and Highway Safety Division.
Model 2070 Controller. The model 2070 controller is one member of the new Advanced Transportation Controller (ATC) family. The ATC is being developed to provide an open architecture hardware and software platform for a wide variety of ITS applications. The development of the ATC is a joint effort sponsored by the Institute of Transportation Engineers (ITE), American Association of State Highway and Transportation Officials (AASHTO), National Electrical Manufacturers Association (NEMA), and the Federal Highway Administration (FHWA).
3/15/02 §11.3.5 11-192 SIGNS, SIGNALS, AND DELINEATION
Modem. A modulator/demodulator device that prepares data for transmission and accepts data at reception. It provides an interface between a computer and the field equipment, such as the traffic signal controllers.
Multiplexing. A communications technique which allows more than one item of information to be transmitted or received over one communication channel.
NEMA. National Electrical Manufacturers Association.
Nonactuated Phase. Traffic signal phase without detection. Nonactuated phases must have the memory/recall on the controller placed on Recall Green.
Nonlocking Detection Memory. A controller feature that sets phases through loop-occupancy control using large-area presence detectors. Waiting calls are dropped when vehicles leave the detection zone.
Nondirectional Detector. A detector capable of being actuated by vehicles traveling in either direction.
Occupancy. The percent of time that a point on the roadway is occupied by a vehicle.
Offset. The time relationship expressed in seconds or percent of cycle length, determined by the difference between a defined interval portion of the coordinated phase green and a system reference point.
Open-Loop Signal System. A system that supervises the intersection controller functions but does not receive feedback information.
Opposing Phase. A phase which permits a conflicting movement.
Overlap. An indication that allows a specific traffic movement through two or more traffic phases. The overlap must not conflict with current running traffic movements.
Pedestrian (WALK) Interval. The interval used to initiate the pedestrian crossing phase.
Pedestrian Clearance (Flashing DONT WALK) Interval. The interval that provides time for a pedestrian to travel from the curb to the center of the far lane before opposing vehicles receive a green indication.
Pedestrian Detector (Push-button). A pole-mounted momentary contact switch which, when activated by a pedestrian, causes a pulse which registers the demand by a pedestrian for the right of way.
Pedestrian Phase. A traffic phase allocated to pedestrian traffic which may provide a right of way indication either concurrently with one or more vehicular phases, or to the exclusion of all vehicular phases.
§11.3.5 3/15/02 SIGNS, SIGNALS, AND DELINEATION 11-193
Pedestrian Recall. The phase memory/recall position which provides a demand resulting in a minimum time equal to a pedestrian "WALK" plus a flashing "DONT WALK" pedestrian clearance interval.
Phase. A portion of a signal cycle during which an assignment of right of way is made to a given traffic movement(s). It includes green and clearance indications.
Phase Sequence. The order in which a signal cycles through all phases.
Point Detection. The detection of vehicles as they pass a specific point on the roadway. Frequently referred to as small-area detection.
Powerhead Loop Detection. The detector configuration that has increased detection sensitivity for small vehicles. It uses small internal loops of wire at the stopline end of long loops.
Preemption. The interruption of normal signal operation to provide for railroad, drawbridge, emergency vehicle, or other unusual operation.
Presence Detection. The sensing of a stationary or slow moving vehicle over a detector. The pulse duration is equal to the actual time the vehicle remains in the detection field of influence.
Presence Loop Detector. An induction loop detector which is capable of detecting the presence of a standing or moving vehicle in any portion of the effective loop area.
Pretimed Signal. A traffic signal for which cycle lengths and phase intervals are established by a predetermined time schedule.
Primary Vehicular Signal Face. A vehicular signal face intended to control through traffic on an intersection approach and located for optimal visibility as per the NYS MUTCD.
Progression. A term used to describe the progressive movement of traffic through several intersections within a control system without stopping.
Pull Box. A container to house cable splices and conduit ends that are placed underground. It also breaks up long cable and conduit runs to facilitate maintenance.
Pulse Mode. A short output pulse produced when detection occurs. The pulse lasts about 100 milliseconds (ms), even if the vehicle remains in the detection zone for a longer time.
Quadrupole. A loop configuration that adds a longitudinal saw cut along the center of the rectangle, so that the wire can be installed in a rectangular figure-eight pattern, thereby producing four electromagnetic poles instead of the normal two. The design improves the sensitivity to small vehicles and also minimizes splashover.
3/15/02 §11.3.5 11-194 SIGNS, SIGNALS, AND DELINEATION
Queue Detector. (1) A vehicle presence detector installed on an entrance ramp just downstream of a frontage road to detect potential queue spillback onto the frontage road. (2) A component of a traffic control system which senses the presence (or number) of vehicles waiting in a queue.
Radar/Microwave Detector. A pole-mounted device that can sense speed and passage and/or presence when activated by a vehicle passing through its radio-frequency (RF) field.
Radio-Frequency Detector. A vehicle detector consisting of a loop of wire embedded in the roadway that is tuned to receive a preselected radio frequency from a transmitter normally located on a bus or emergency vehicle.
Ramp Metering. A method of freeway traffic control that regulates the number of vehicles entering the freeway over a given time interval so that demand does not exceed capacity.
Ramp Metering Signal. A traffic signal which directs entrance ramp vehicles to stop and permits them to proceed in accordance with metering rates determined by the type of entrance ramp control being used.
Recall. An operational mode for an actuated controller unit whereby a phase, either vehicle or pedestrian, is displayed each cycle whether or not demand exists. It is usually for a temporary or emergency situation.
Recall Green. The phase memory/recall position in the Model 170/179 controller which provides a demand resulting in a given programmable fixed-green time.
Red Clearance Interval. It follows the yellow change interval. Both terminating phase and conflicting phases display red.
Red Revert. The fixed minimum red signal indication time prior to returning to a phase just terminated.
Rest-In-Red. A control designed to display red to all movements, in the absence of any traffic demand.
Reversible Lane. A term used to describe a traffic lane upon which the direction of the flow of traffic may be varied during different periods of the day.
Sampling Detector. Any type of vehicle detector used to obtain representative traffic flow information for signal system coordination.
Secondary Vehicular Signal Face. A vehicular signal face intended to control only traffic in an auxiliary lane or other nonpredominant traffic movement
Self-Powered Vehicle Detection. An in-road detection device, currently in development, that does not require lead-in or interconnecting cables. It uses an internal battery and Radio-Frequency (RF) link.
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Self-Tracking Detector. A loop detector unit, not necessarily self-tuning, that includes electronics that compensate for environmental drift. Environmental drift is the drift in the resonant frequency of the detector caused by changes in temperature and moisture.
Self-Tuning Loop Detector Unit. One that is capable of adapting its operation to the resonant frequency of the loop and lead-in wire without any manual adjustment required. The term applies particularly to the startup of the detector's operation upon turn on.
Semiactuated Traffic Operation. A traffic signal operation in which means are provided for traffic actuation on one or more, but not all, approaches to an intersection.
Sensitivity. As it relates to a loop system, it is the change in the total induction of a system caused by a minimum vehicle at one loop, expressed as a percentage of the total inductance. As it relates to a detector, it is the minimum inductance change, in percent, required at the input terminals to actuate the detector.
Sensor. Traffic detection devices (detector) that informs the system master or a local controller as to the traffic characteristics in the area of the sensor.
Shield. A conductive material surrounding the pair of lead-in wires of a loop detector installation, so that outside electrical interference will not induce interference in them.
Signal Indication. The illumination of a signal lens (or an equivalent device) controlling the movement of vehicular or pedestrian traffic.
Signal Timing. The amount of time allocated to each interval/function in a signal cycle.
Single Entry. A fully actuated operating mode in a dual ring in which a phase in one ring can be selected and timed alone when there is no demand for service in a nonconflicting phase or a parallel ring. The software for the Models 170 and 179 controllers is configured as single- entry controllers.
Skip Phasing. The ability of a controller unit to omit a phase in the absence of demand on that phase or as directed by a master control. The Models 170/179 controller software has this capability.
Small-Area Detectors. Devices that detect vehicle passage at spot locations. Also called short- loop, point, or passage detectors.
Sonic Detector (Active). A pole-mounted device that transmits/receives ultrasonic pulses to determine a vehicle’s presence.
Sonic Detector (Passive). A mounted acoustic device that listens to vehicle generated noise to establish presence and passage. May provide vehicle type based on noise spectrum.
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Splashover. An unwanted actuation caused by a vehicle in a lane adjacent to that in which the detector is located.
Split. The percentage of a cycle length allocated to each of the various phases.
Stretch Detector (Extended Call Detector). A detector that holds or stretches the call of a vehicle for a period of seconds that has been set on an adjustable timer.
Supplemental Vehicular Signal Face. A vehicular signal face in addition to the required primary and secondary vehicular signal face.
Time-Based Signal Coordination. A controller coordination technique that changes timing plans on an internal time clock basis. The Model 179 traffic control software has a time-based function included in the controller.
Time-Based Coordination Control (TBC). TBC control permits systems operation of traffic controllers without communication links or master control units.
Time Before Reduction. The time interval commencing with an opposing call before the maximum gap begins to be reduced.
Time-Of-Day Operation. Signal timing plans or signal operation selected according to the time of day.
Time To Reduce. The time it takes to reduce from maximum allowable gap to the minimum allowable gap.
Traffic-Actuated Operation. It assigns right of way and determines the cycle length and phases, based on the detection of traffic on the various approaches.
Traffic Control Signal. A highway traffic signal by which traffic is alternately directed to stop and permitted to proceed. A traffic control signal is sometimes referred to as a three-color signal or a stop-and-go signal.
Traffic Phase. Those green, yellow, and all red intervals in a cycle assigned to any independent movement(s) of traffic.
Traffic Signal System. A signal system that controls a group of arterial or surface street networks through coordinated traffic signals. There are two types of traffic signal systems: arterial and closed grid network systems.
Upstream. The roadway portion which is positioned toward the source of approaching traffic from the point of reference.
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Variable Initial. A value which is automatically multiplied by the number of vehicles passing the detector on the previous red interval to provide sufficient time to clear all vehicles queued between the detector and stop line at the onset of green (see Initial Vehicle Interval).
Vehicle Detection System. A system for indicating the presence or passage of a vehicle.
Yellow Change Interval. The interval following green that alerts motorists to imminent phase termination.
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11.3.6 References
The following is a list of the publications and other sources of information used in the preparation of the Signals portion of this chapter.
1. Detector Location, Safety Operations Unit Publication 12, December 1982, Traffic Engineering and Highway Safety Division, New York State Department of Transportation, 1220 Washington Avenue, Albany, NY 12232
2. Evaluation of Rest-In-Red Signal Operation, Safety Operations Unit Publication 9, May 1982, Traffic Engineering and Highway Safety Division, New York State Department of Transportation, 1220 Washington Avenue, Albany, NY 12232
3. GATER: Model 179 Ramp Metering Software Program, Traffic Engineering and Highway Safety Division, New York State Department of Transportation, 1220 Washington Avenue, Albany, NY 12232
4. Manual of Traffic Signal Design, Institute of Transportation Engineers, 525 School Street, SW, Suite 410, Washington, DC 20024-2729
5. Model 215 Current Monitor For Model 330 Cabinets, April 24, 1986 Memorandum D.J. Russo to All Regional Traffic Engineers, Traffic Engineering and Highway Safety Division, New York State Department of Transportation, 1220 Washington Avenue, Albany, NY 12232
6. New York State Standard Sheets (Metric Units), Plan Sales Unit, New York State Department of Transportation, 1220 Washington Avenue, Albany, NY 12232
7. Vehicle and Traffic Law, (latest edition), State of New York State Commissioner of Motor Vehicles, 6 Empire State Plaza, Albany, NY 12228
8. Signal Installation, September 1981, Traffic Engineering and Highway Safety Division, New York State Department of Transportation, 1220 Washington Avenue, Albany, NY 12232
9. Signalized Intersection Design Course, Traffic Engineering and Highway Safety Division, New York State Department of Transportation, 1220 Washington Avenue, Albany, NY 12232
10. Standard Specifications, Construction and Materials (Metric Units), Plan Sales Unit, New York State Department of Transportation, 1220 Washington Avenue, Albany, NY 12232
11. Technical Note 82-2, Leading vs. Lagging Left Turns, October 1982, Traffic Engineering and Highway Safety Division, New York State Department of Transportation, 1220 Washington Avenue, Albany, NY 12232
12. Technical Note 82-3, Protected and Protected/Permissive Left Turns, October 1982, Traffic Engineering and Highway Safety Division, New York State Department of Transportation, 1220 Washington Avenue, Albany, NY 12232
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13. Title 17, Volume B of the Official Compilation of Codes, Rules and Regulations of the State of New York (NYCRR), also known as the New York State Manual of Uniform Traffic Control Devices, West Group, 620 Opperman Drive, PO Box 64833, St. Paul, MN 55164-9752
14. Traffic Control Systems Handbook, Publication No. FHWA-SA-95-032, 1996, US Department of Transportation Federal Highway Administration, Office of Technology Applications, 400 Seventh Street, SW, Washington, DC 20590
15. Traffic Actuated Processing System, Operators Manual, January 1, 1998, Traffic Engineering and Highway Safety Division, NewYork State Department of Transportation, 1220 Washington Avenue, Albany, NY 12232
16. Traffic Detectors Student Manual, US Department of Transportation Federal Highway Administration, Office of Technology Applications, 400 Seventh Street, SW, Washington, DC 20590
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APPENDICIES
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