Flow Signals Aid Traffic in Houston

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TEXAS TRANSPORTATION INSTITUTE For More Details … THE TEXAS A&M UNIVERSITY SYSTEM The research described is documented in the following research reports: Project Summary Report 1295-S Project 0-1295: Ramp Metering in Houston, Texas Report 1295-1, “Go with the Flow Houston Ð A Public Outreach Plan” Author: Carroll J. Messer, P.E. Report 1295-2, “A Dual-Lane Flow Signal Plan for Texas”

Research Supervisor: Carroll J. Messer, P.E., TTI, (979) 845-9893, [email protected] Researchers: Steve Wohlschlaeger, Susan Lancaster, and Marc Butorac TxDOT Project Director: John Gaynor, P.E., HOU (713) 881-3060 Flow Signals Aid Traffic in Houston

To obtain copies of these reports, contact Dolores Hott, Texas Transportation Institute, Information & Technology Exchange Center, (979) 845-4853, or e-mail [email protected]. See our catalog on-line at http://tti.tamu.edu. To reduce traffic congestion, What We Did . . . approached in 1996. The air pollution, and traffic Ramp metering was term “Flow Signals” was accidents occurring in Texas implemented on five freeways effectively used in public cities, the Texas Department of in Houston with nearly 100 information, TV spots, and TxDOT Implementation Status Transportation (TxDOT) has ramps now being metered. newspaper announcements in reintroduced ramp metering as The first meters were activated Houston. Project report July 2000 “flow signals” based on the along an inbound section of 1295-1 provides details of the TxDOT has already implemented, as part of this research, an enhanced ramp meter controller in Houston. Dual-lane quality of service provided. IH-10 (Katy Freeway) on July very successful “Flow metering can provide nearly twice the ramp metering and queue storage capacity. This is an important feature in This project supported the 31, 1996, with a systematic Signals” marketing program. Texas where relatively high ramp volumes and short slip ramps are often present. TxDOT has concurrently updated implementation and testing of expansion on additional The Houston District ramp meter specification to permit future purchase of this advanced controller where justified. basic ramp metering strategies freeways into 1999. developed methods to in Houston, Texas, as a part A large-scale marketing remotely operate and observe TxDOT has been provided with the following products to assist traffic engineers with implementation of of TxDOT’s ongoing and public information different operating strategies dual-lane metering at a specific location: implementation program for program was planned and in a real world environment ¥ public information campaign to be used for reference if needed; improved freeway traffic pursued as the first ramp in support of this work. ¥ determination that law enforcement did not become a significant issue in Houston; management. metering implementation date ¥ improved guidelines that identify volumes which would warrant use of dual-lane metering; and What We Found . . . ¥ recommended detector layouts, controller timings, and traffic control devices (signs and Both the general public markings) to use with dual-lane metering. and TxDOT judged the Contact: John Bassett, P.E., CSTR Research Engineer, (512) 465-7922 or e-mail [email protected]. overall ramp-metering program to be successful. The initial ramp meters were YOUR INVOLVEMENT IS WELCOME! all single-lane designs, releasing one vehicle per This research was performed in cooperation with the Texas Department of Transportation and the U.S. Department of green signal and providing a Transportation, Federal Highway Administration. The contents of this report reflect the views of the author, who is metering capacity of about responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official 800 vehicles per hour (vph). view or policies of the FHWA or TxDOT. This report does not constitute a standard, specification, or regulation, nor is it These meters are similar to

PROJECT SUMMARY REPORT intended for construction, bidding, or permit purposes. Trade names are used solely for information and not for product those deployed in Texas in endorsement. The engineer in charge was Carroll J. Messer, P.E. (Texas 31409). the late 1960s. One major challenge faced by the ramp metering effort was the high Figure 1. Dual-Lane Ramp Metering in Houston

Project Summary Report 1295-S – 4 – Project Summary Report 1295-S – 1 – entrance ramp demand volumes shows the FM 1960 dual-lane ramp (b) platoon metering (with 2-3 Researchers should be designed for dual-lane, developed to provide a cost- observed in Houston. Many in operation. No public complaints vehicles/per green) may serve Recommend . . . single-entry metering, and effective geometric design for the standard freeway slip-ramp designs have been received regarding this up to about 1050-1150 vph Ramp metering should be projected ramp volumes exceeding “warranted” entrance ramps, had ramp demand volumes in the ramp since it began operation. In before either unreliable ramp considered as a viable freeway 1600 vph should be designed for including ramp cross section, 1300-1600 vph range during fact, many comments were operation begins, or ramp traffic management tool for use in dual-lane metering with dual-entry number of lanes, and overall ramp metering periods, with several even received from concerned motorists vehicles begin violating the all Texas metropolitan areas. ramp connections. Another spacing from the upstream exceeding these high volume levels. during reconstruction from single- signal’s operation; and Selection of the type of ramp metering option would be to permit interchange/frontage road Faced with high ramp demands, lane to dual-lane metering to not metering strategy should be based higher ramp delays thereby connection to the downstream an investigation of metering permanently turn off the ramp (c) dual-lane metering with on the expected ramp volumes to encouraging more ramp diversion freeway merge point to adequately strategies used by other states meter. Demand volumes at the FM single-lane merging can be served. Dual-lane metering in cases where good alternate store vehicles queued behind the revealed that New York employed 1960 ramp are now higher and a reliably meter ramp volumes with single-entry merge and dual- routes exist. meter. Research should be a “queued off” strategy when dual-lane ramp entry design may as high as 1600 vph if the lane metering with dual-entry Urban freeway design of conducted to develop the criteria ramps became overloaded. A be needed to reliably meter such freeway has adequate connection should be used where entrance ramps in Texas should and guidelines needed to achieve similar strategy is used in Houston, high volumes. downstream capacity. ramp volumes warrant. Ramp consider the type of ramp metering these objectives. wherein an upstream ramp queue A theoretical model was volumes between 1200 - 1600 vph warranted. Procedures should be detector will sense excessive developed to explain the ramp Minnesota Department of queue formation and then flush volume challenges faced in Transportation (DOT) has found any excessive queue to avoid Houston. This model predicts the that ramp demand volumes queue spillback into upstream percent of time the meter operates exceeding 1600 vph will routinely interchanges and excessive ramp nominally (its availability to meter queue off even dual-lane meters. delays. Otherwise, the meters are routinely), as shown in Figure 2. In such cases, a higher-type timed to operate such that an Three types of ramp metering are freeway ramp entry design should arriving motorists ramp access examined in Figure 2, including the be considered, such as providing a time to the freeway does not traditional single-lane meter, dual-lane, dual-entry connection to exceed 2.0 minutes. platoon (bulk service) metering on the downstream freeway. The With many ramps in Houston single-lane ramps, and dual-lane freeway metering assessments having demand volumes exceeding metering necking down beyond the (Good, Fair, and Fail) shown in single-lane metering capacity of meter into a single merge lane. Figure 2 are from Minnesota DOT 800 vph, higher capacity ramp The dual-lane meter has a nominal based on its nearly 30 years of meter designs were investigated. maximum metering rate of about operational experience with ramp Dual-lane metering into a single- 1600 vph and a ramp flush rate for metering. lane merge was developed and short time periods of about 1800 Functional controller upgrades, tested at the interchange of US 290 vph. Dual-lane metering having including dual-lane ramp metering, with FM 1960/TX 6 located in dual-entry lanes onto the freeway were prepared for TxDOT’s northwest Houston, starting in was not studied in this research. existing 1997 ramp metering October 1998. This design has a This option would require major controller (RMC) specification. nominal metering capacity of geometric design changes TxDOT recently purchased and about 1600 vph, subject to site- downstream of entrance ramps. deployed several RMC upgrades in specific downstream freeway Figure 2 also shows that: Houston, including the FM 1960 capacity. Dual-lane metering has dual-lane meter shown in Figure 1. worked very well at this site where (a) single-lane metering can For more details on this dual-lane Figure 2. Performance of Metering Strategies with Ramp Demand Volume a neck-down diamond ramp (over reliably serve ramp demand design, see project report 1295-2. 1200 feet long) without frontage volumes up to about 800 vph; roads was available. Figure 1

Project Summary Report 1295-S – 2 – Project Summary Report 1295-S – 3 – entrance ramp demand volumes shows the FM 1960 dual-lane ramp (b) platoon metering (with 2-3 Researchers should be designed for dual-lane, developed to provide a cost- observed in Houston. Many in operation. No public complaints vehicles/per green) may serve Recommend . . . single-entry metering, and effective geometric design for the standard freeway slip-ramp designs have been received regarding this up to about 1050-1150 vph Ramp metering should be projected ramp volumes exceeding “warranted” entrance ramps, had ramp demand volumes in the ramp since it began operation. In before either unreliable ramp considered as a viable freeway 1600 vph should be designed for including ramp cross section, 1300-1600 vph range during fact, many comments were operation begins, or ramp traffic management tool for use in dual-lane metering with dual-entry number of lanes, and overall ramp metering periods, with several even received from concerned motorists vehicles begin violating the all Texas metropolitan areas. ramp connections. Another spacing from the upstream exceeding these high volume levels. during reconstruction from single- signal’s operation; and Selection of the type of ramp metering option would be to permit interchange/frontage road Faced with high ramp demands, lane to dual-lane metering to not metering strategy should be based higher ramp delays thereby connection to the downstream an investigation of metering permanently turn off the ramp (c) dual-lane metering with on the expected ramp volumes to encouraging more ramp diversion freeway merge point to adequately strategies used by other states meter. Demand volumes at the FM single-lane merging can be served. Dual-lane metering in cases where good alternate store vehicles queued behind the revealed that New York employed 1960 ramp are now higher and a reliably meter ramp volumes with single-entry merge and dual- routes exist. meter. Research should be a “queued off” strategy when dual-lane ramp entry design may as high as 1600 vph if the lane metering with dual-entry Urban freeway design of conducted to develop the criteria ramps became overloaded. A be needed to reliably meter such freeway has adequate connection should be used where entrance ramps in Texas should and guidelines needed to achieve similar strategy is used in Houston, high volumes. downstream capacity. ramp volumes warrant. Ramp consider the type of ramp metering these objectives. wherein an upstream ramp queue A theoretical model was volumes between 1200 - 1600 vph warranted. Procedures should be detector will sense excessive developed to explain the ramp Minnesota Department of queue formation and then flush volume challenges faced in Transportation (DOT) has found any excessive queue to avoid Houston. This model predicts the that ramp demand volumes queue spillback into upstream percent of time the meter operates exceeding 1600 vph will routinely interchanges and excessive ramp nominally (its availability to meter queue off even dual-lane meters. delays. Otherwise, the meters are routinely), as shown in Figure 2. In such cases, a higher-type timed to operate such that an Three types of ramp metering are freeway ramp entry design should arriving motorists ramp access examined in Figure 2, including the be considered, such as providing a time to the freeway does not traditional single-lane meter, dual-lane, dual-entry connection to exceed 2.0 minutes. platoon (bulk service) metering on the downstream freeway. The With many ramps in Houston single-lane ramps, and dual-lane freeway metering assessments having demand volumes exceeding metering necking down beyond the (Good, Fair, and Fail) shown in single-lane metering capacity of meter into a single merge lane. Figure 2 are from Minnesota DOT 800 vph, higher capacity ramp The dual-lane meter has a nominal based on its nearly 30 years of meter designs were investigated. maximum metering rate of about operational experience with ramp Dual-lane metering into a single- 1600 vph and a ramp flush rate for metering. lane merge was developed and short time periods of about 1800 Functional controller upgrades, tested at the interchange of US 290 vph. Dual-lane metering having including dual-lane ramp metering, with FM 1960/TX 6 located in dual-entry lanes onto the freeway were prepared for TxDOT’s northwest Houston, starting in was not studied in this research. existing 1997 ramp metering October 1998. This design has a This option would require major controller (RMC) specification. nominal metering capacity of geometric design changes TxDOT recently purchased and about 1600 vph, subject to site- downstream of entrance ramps. deployed several RMC upgrades in specific downstream freeway Figure 2 also shows that: Houston, including the FM 1960 capacity. Dual-lane metering has dual-lane meter shown in Figure 1. worked very well at this site where (a) single-lane metering can For more details on this dual-lane Figure 2. Performance of Metering Strategies with Ramp Demand Volume a neck-down diamond ramp (over reliably serve ramp demand design, see project report 1295-2. 1200 feet long) without frontage volumes up to about 800 vph; roads was available. Figure 1

Project Summary Report 1295-S – 2 – Project Summary Report 1295-S – 3 – TEXAS TRANSPORTATION INSTITUTE For More Details … THE TEXAS A&M UNIVERSITY SYSTEM The research described is documented in the following research reports: Project Summary Report 1295-S Project 0-1295: Ramp Metering in Houston, Texas Report 1295-1, “Go with the Flow Houston Ð A Public Outreach Plan” Author: Carroll J. Messer, P.E. Report 1295-2, “A Dual-Lane Flow Signal Plan for Texas”

Project Summary Report 1295-S – 4 – Project Summary Report 1295-S – 1 –