HIGHWAY DESIGN MANUAL 500-1 July 1, 2015

• Projects to increase mainline capacity when CHAPTER 500 existing interchanges do not meet interchange TRAFFIC INTERCHANGES spacing requirements. See Index 504.7 for additional technical requirements Topic 501 - General related to interchange spacing. Procedures and documentation requirements are provided in PDPM Index 501.1 - Concepts Chapter 27. See the FHWA publication “Interstate A traffic interchange is a combination of ramps and System Access Informational Guide.” grade separations at the junction of two or more highways for the purpose of reducing or eliminating Topic 502 - Interchange Types traffic conflicts, to improve safety, and increase traffic capacity. Crossing conflicts are reduced by 502.1 General grade separations. Turning conflicts are either The selection of an interchange type and its design eliminated or minimized, depending upon the type of are influenced by many factors including the interchange design. following: speed, volume, and composition of traffic 501.2 Warrants to be served (e.g., trucks, vehicles, bicycles, and pedestrians), number of intersecting legs, and All connections to freeways are by traffic arrangement of the local street system (e.g., traffic interchanges. An interchange or separation may be control devices, topography, right of way controls), warranted as part of an expressway (or in special local planning, proximity of adjacent interchanges, cases at the junction of two non-access controlled community impact, and cost. highways), to improve safety or eliminate a The cost of a structure is a considerable investment bottleneck, or where topography does not lend itself where the life of a structure may be 50 to 100 years, to the construction of an intersection. far beyond that of the project traffic study 501.3 Spacing projections. New or significant modifications to interchanges should take into consideration future The minimum interchange spacing shall be needs of the system; the ultimate configuration for one mile in urban areas, two miles outside of the freeway and the potential for local land urban areas, and two miles between freeway-to- development well beyond the 20-year traffic study. freeway interchanges and other interchanges. The Choose an interchange type that is compatible with minimum interchange spacing on Interstates or can easily be modified to accommodate the future outside of urban areas shall be three miles. These growth of the system. minimum distances are measured between centerlines of adjacent intersecting roadways. To Even though interchanges are designed to fit specific improve operations of closely spaced interchanges conditions and controls, it is desirable that the pattern the use of auxiliary lanes, grade separated ramps, of interchange ramps along a freeway follow some collector-distributor roads, and/or ramp metering degree of consistency. It is frequently desirable to may be warranted. rearrange portions of the local street system in connection with freeway construction in The standards contained within this Index apply to: • New interchanges. • Modifications to existing interchanges including access control revisions for new ramps or the relocation/elimination of existing ramps. 500-2 HIGHWAY DESIGN MANUAL December 30, 2015 order to affect the most desirable overall plan for the least impact on those users most affected by the mobility and community development. elevation changes, such as pedestrians and bicyclists. Interchange types are characterized by the basic Class II bikeways designed through interchanges shapes of ramps: namely, diamond, loop, directional, should be accomplished considering the mobility of hook, or variations of these types. Many interchange bicyclists and should be designed in a manner that designs are combinations of these basic types. will minimize confusion by motorists and bicyclists. Schematic interchange patterns are illustrated in Designs which allow high speed merges at on- and Figure 502.2 and Figure 502.3. These are classified off-ramps to local streets and conventional highways as: (a) Local street interchanges and (b) Freeway-to- have a large impact on bicycle and pedestrian freeway interchanges. See AASHTO, A Policy on mobility and should not be used. Designers should Geometric Design of Highways and Streets, for work closely with the Local Agency when designing additional examples. bicycle facilities through interchanges to ensure that the shoulder width is not reduced through the 502.2 Local Street Interchanges interchange area. If maintaining a consistent The Department’s philosophy for highway design shoulder width is not feasible, the Class II bikeway has evolved over time. DD-64 Complete Streets, DP- must end at the previous local road intersection. A 22 Context Sensitive Solutions, DP-05 Multimodal solution on how to best provide for bicycle travel to Alternatives and other policies and guidance are a connect both sides of the freeway should be result of that evolution in design philosophy. No developed in consultation with the Local Agency and longer are freeway interchanges designed with only community as well as with the consideration of the the needs of motorists in mind. Pedestrian and local bicycle plan. bicycle traffic needs are to be considered along with (a) Diamond Interchange--The simplest form of the motorized traffic. Local road interchanges ramp interchange is the diamond. Diamond termini should be perpendicular to the local road. interchanges provide a high standard of ramp The high speed, shallow angle, ramp termini of the alignment, direct turning maneuvers at the past are problematic for pedestrians and bicyclists to crossroads, and usually have minimum navigate. Vehicle speeds are reduced by the right construction costs. The diamond type is angle turn, allowing drivers to better respond to adaptable to a wide range of traffic volumes, as bicycle and pedestrian conflicts. For new well as the needs of transit, bicyclists, and construction or major reconstruction consideration pedestrians. The capacity is limited by the must be given to orienting ramps at right angles to capacity of the intersection of the ramps at the local streets. For freeways where bicycles are crossroad. This capacity may be increased by permitted to us the freeway, ramps need to be widening the ramps to two or three lanes at the designed so that bicyclists can exit and enter the crossroad and by widening the crossroad in the freeway without crossing the higher speed ramp intersection area. Crossroad widening will traffic. See Index 400 for type, design, and capacity increase the length of undercrossings and the of intersections at the ramp terminus with the local width of overcrossings, thus adding to the bridge road. cost. Roundabouts may provide the necessary An interchange is expected to have an on- and off- capacity without expensive crossroad widening ramp for each direction of travel. If an off-ramp does between the ramp termini. Ramp intersection not have a corresponding on-ramp, that off-ramp capacity analysis is discussed in Topic 406. would be considered an isolated off-ramp. Isolated The compact diamond (Type L-1) is most off-ramps or partial interchanges shall not be adaptable where the freeway is depressed or used because of the potential for wrong-way movements. In general, interchanges with all ramps connecting with a single cross street are preferred. At local road interchanges it is preferable to minimize elevation changes on the local road and instead elevate or depress the freeway. Such designs have HIGHWAY DESIGN MANUAL 500-3 May 7, 2012

Figure 502.2 Typical Local Street Interchanges 500-4 HIGHWAY DESIGN MANUAL May 7, 2012

Figure 502.2 Typical Local Street Interchanges (continued) HIGHWAY DESIGN MANUAL 500-5 May 7, 2012

elevated and the cross street retains a straight Special attention should always be given to exit profile. Type L-1's are suitable where physical, ramps that end in a hook to ensure that adequate geometric or right of way restrictions do not sight distance around the curve, adequate permit a spread diamond configuration. deceleration length prior to the curve or end of Compact diamonds have the disadvantage of anticipated queue, and adequate superelevation requiring wider overcrossing or longer span for anticipated driving speeds can be developed. undercrossing to provide corner sight distance Type L-6 can only be considered when all other and have limited capacity between intersections. interchange types are not acceptable. Once the area around the interchange is (c) Cloverleaf Interchanges--The simplest cloverleaf developed, Type L-1 is challenging to expand to interchange is the two-quadrant cloverleaf, Type accommodate growth. L-7 or Type L-8, or a combination where the two The spread diamond (Type L-2) is adaptable loops are on the same side of the cross street. where the grade of the cross street is changed to Type L-7 eliminates the need for left-turn storage pass over or under the freeway. The ramp lanes, on or under the structure, thus reducing the terminals are spread in order to achieve structure costs. These interchanges should be maximum sight distance and minimum used only in connection with controls which intersection cross slope, commensurate with preclude the use of diamond ramps in all four construction and right of way costs, travel quadrants. These controls include right of way distance, and general appearance. A spread controls, a railroad track paralleling the cross diamond has the advantage of flatter ramp street, and a short weaving distance to the next grades, greater crossroads left-turn storage interchange. capacity, and the flexibility of permitting the The Type L-9, partial cloverleaf interchange, construction of future loop ramps if required. provides loop on-ramps in addition to the four The split diamond with braids (Type L-3) may be diamond-type ramps. This interchange is appropriate where two major crossroads are suitable for large volume turning movements. closely spaced. Left-turn movements from the crossroads are eliminated, thereby permitting two-phase (b) Interchanges with Parallel Street Systems--Types operation at the ramp intersections when L-4, L-5 and L-6 are interchange systems used signalized. Because of this feature, the Type L- where the freeway alignment is placed between 9 interchange usually has capacity to handle the parallel streets. Types L-4 and L-5 are used higher volume traffic on the crossroad. where the parallel streets will operate with one- way traffic. In Type L-4 slip ramps merge with The four-quadrant cloverleaf interchange (Type the frontage street and in Type L-5 the ramps L-10) offers free-flow characteristics for all terminate at the intersection of the frontage road movements. It has the disadvantage of a higher with the cross street, forming five-legged cost than a diamond or partial cloverleaf design, intersections. In Type L-6 the freeway ramps as well as a relatively short weaving section connect with two-way parallel streets. The between the loop ramps which limits capacity. parallel streets in the Types L-4, L-5 and L-6 For this reason this type of interchange is not situation are usually too close to the freeway to desirable. Collector-distributor roads should be permit ramp intersections on the cross street incorporated in the design of four-quadrant between the parallel frontage streets. cloverleaf interchanges to separate the weaving conflicts from the through freeway traffic. The "hook" ramps of the Type L-6 are often forced into tight situations that lead to less than (d) Trumpet Interchanges--A trumpet design, Type desirable geometrics. The radius of the curve at L-11 or L-12, may be used when a crossroads the approach to the intersection should exceed terminates at a freeway. This design should not 150 feet and a tangent of at least 150 feet should be used if future extension of the crossroads is be provided between the last curve on the ramp probable. The diamond interchange is and the ramp terminal. 500-6 HIGHWAY DESIGN MANUAL December 14, 2018

preferable if future extension of the crossroads is the interchange configuration shall keep the expected. designated route to the left through the interchange. (e) Single Point Interchange (SPI)--The Type L-13 is a concept which essentially combines two (2) Design Considerations. separate diamond ramp intersections into one (a) Cost--The differential cost between large at-grade intersection. It is also known as an interchange types is often significant. A urban interchange. Additional information on cost-effective approach will tend to assure SPI’s is provided in DIB 92 “Single Point that an interchange is neither over nor Interchange Guidelines.” underdesigned. Decisions as to the relative Type L-13 requires approximately the same right values of the previously mentioned of way as the compact diamond. However, the parameters must be consistent with construction cost is substantially higher due to decisions reached on adjacent main line the structure requirements. The capacity of the freeways. L-13 can exceed that of a compact diamond if (b) System Balance--The freeway-to-freeway long signal times can be provided and left turning interchange is a critical link in the total volumes are balanced. freeway system. The level of traffic service This additional capacity may be offset if nearby provided will have impact upon the intersection queues interfere with weaving and mobility and overall effectiveness of the storage between intersections. The entire roadway system. For instance, traffic disadvantages of the L-13 are: 1) future patterns will adjust to avoid repetitive expansion of the interchange is extremely bottlenecks, and to the greatest degree difficult; 2) stage construction for retrofit possible, to temporary closures, accidents, situations is costly; 3) long structure spans etc. The freeway-to-freeway interchange require higher than normal profiles and deeper should provide flexibility to respond to structure depths; and 4) longer bicycle and these needs so as to maximize the cost pedestrian circulation. effectiveness of the total system. (f) Other Types of Interchanges--New or (c) Provide for all Traffic Movements--All experimental interchanges must have the Project interchanges must provide for each of the Delivery Coordinator and the Headquarters eight basic movements (or four basic Chief, Division of Traffic Operations movements in the case of a three-legged concurrence before selection. Concurrence may interchange), except in the most extreme require additional studies and documentation. circumstances. Less than “full interchanges” may be considered on a case- 502.3 Freeway-to-Freeway Interchanges by-case basis for applications requiring (1) General. The function of the freeway-to- special access for managed lanes (e.g., freeway interchange is to link freeway segments transit, HOVs, HOT lanes) or park and together so as to provide the highest level of ride lots. Partial interchanges usually service in terms of mobility. Parameters such as have undesirable operational cost, environment, community values, traffic characteristics. If circumstances exist volumes, route continuity, driver expectation where a partial interchange is considered and safety should all be considered. Route appropriate as an initial phase continuity, providing for the designated route to improvement, then commitments need to continue as the through movement through an be included in the request to accommodate interchange, reduces lane changes, simplifies the ultimate design. These commitments signing, and reduces driver confusion. may include purchasing the right of way Interstate routes shall maintain route continuity. Where both the designated route and heavier traffic volume route are present, HIGHWAY DESIGN MANUAL 500-7 March 7, 2014

required during the initial phase (3) Types. Several freeway-to-freeway interchange improvements. design configurations are shown on Figure 502.3. Many combinations and variations may (d) Local Traffic Service--In metropolitan be formed from these basic interchange types. areas a freeway-to-freeway interchange is usually superimposed over an existing (a) Four-Level-Interchange--Direct street system. Local and through traffic connections are appropriate in lieu of loops requirements are often in conflict. when required by traffic demands or other specific site conditions. The Type F-1 Combinations of local and freeway-to- interchange with all direct connections freeway interchanges can result in designs provides the maximum in mobility and that are both costly and so complex that the safety. However, the high costs associated important design concepts of simplicity and with this design require that the benefits be consistency are compromised. Therefore, fully substantiated. alternate plans separating local and freeway-to-freeway interchanges should be The Type F-1 Alternative "A" interchange fully explored. Less than desirable local utilizes a single divergence ramp for traffic interchange spacing may result; however, bound for the other freeway; then provides this may be compensated for by upgrading a secondary directional split. Each entrance the adjacent local interchanges and street ramp on a Type F-1A interchange is system. provided separately. The advantages of the Type F-1A are: 1) reduced driver confusion Local traffic service interchanges should since there is only one exit to the other not be located within freeway-to-freeway freeway, and 2) operations at the entrance interchanges unless geometric standards may be improved since the ramps merge and level of service will be substantially with the mainline one at a time. maintained. The Type F-1 Alternative "B" interchange (e) Alignment--It is not considered practical to provides separate directional exit ramps and establish fixed freeway-to-freeway then merges the entering traffic into a single interchange alignment standards. An ramp before converging with the mainline. interchange must be designed to fit into its Since the Type F-1B combines traffic from environment. Alignment is often controlled two ramps before entering the freeway, it is by external factors such as terrain, important to verify that adequate weaving buildings, street patterns, route adoptions, capacity is provided beyond the entrance. and community value considerations. Separating the directional split of exiting Normally, loops have radii in the range of traffic reduces the volume to each of the two 150 feet to 200 feet and direct connections ramps and therefore may improve the level should have minimum radii of 850 feet. of service of the weave section prior to the Larger radii may be proper in situations exit. where the skew or other site conditions will result in minimal increased costs. Direct Design for a four-level interchange may connection radii of at least 1,150 feet are combine the configuration of the Type F1- desirable from a traffic operational A and F1-B interchange to best suit the standpoint. High alignment and sight conditions at a given location. distance standards should be provided (b) Combination Interchanges--The three- where possible. quadrant cloverleaf, Type F-2, with one Drivers have been conditioned to expect a direct connection may be necessary where certain standard of excellence on California freeways. The designer's challenge is to provide the highest possible standards consistent with cost and level of service. 500-8 HIGHWAY DESIGN MANUAL July 2, 2018

a single move carries too much traffic for a Topic 503 - Interchange Design loop ramp or where the one quadrant is Procedure restricted by environmental, topographic, or right of way controls. 503.1 Basic Data The two-loop, two-direct connection Data relative to community service, traffic, physical interchange, Type F-3, is often an and economic factors, and potential area appropriate solution. The weaving conflicts development which may materially affect design, which ordinarily constitute the most should be obtained prior to interchange design. restrictive traffic constraint are eliminated, Specifically, the following information should be yet cost and right of way requirements may available: be kept within reasonable bounds. Consideration should be given to providing (a) The location and standards of existing and an auxiliary lane in advance of the loop off- proposed local streets including types of traffic ramps to provide for vehicle deceleration. control. (c) Four-Quadrant Cloverleaf--The four- (b) Existing, proposed and potential for development quadrant cloverleaf with collector- of land, including such developments as distributor roads, Type F-4, is ordinarily the employment centers, retail services and shopping most economical freeway-to-freeway centers, recreational facilities, housing interchange solution when all turning developments, schools, and other institutions. movements are provided. The four- (c) A vehicle traffic flow diagram showing average quadrant cloverleaf is generally applicable daily traffic and design hourly volumes, as well in situations where turning volumes are low as time of day (a.m. or p.m.), anticipated on the enough to be accommodated in the short freeway ramps and affected local streets or roads. weaving sections. It should be designed with collector-distributor roads to separate (d) Current and future bicycle and pedestrian access weaving conflicts from the through freeway through the community. traffic. (e) The relationship with adjacent interchanges. (d) Freeway Terminal Junction--Types F-5, (f) The location of major utilities, railroads, or F-6, F-7, and F-8 are examples of airports. interchange designs where one freeway terminates at the junction with another (g) The presence of dedicated lanes and associated freeway. In general, the standard of ramps and connections, including HOV lanes, alignment provided on the left or median Bus (BRT) lanes and Express lanes. lane connection from the terminating (h) The planned ultimate build-out for the freeway freeway should equal or approach as near as facility. possible that of the terminating freeway. Terminating the median lane on a loop (i) Existing and planned rail facilities. should be avoided. It is preferable that both 503.2 Reviews the designated route and the major traffic volume be to the left at the branch Interchanges are among the major design features connection diverge. The choice between which are to be reviewed by the Project Delivery Types F-7 and F-8 should include Coordinator and/or District Design Liaison, District considerations of traffic volumes, and route Traffic Engineer or designee, other Headquarters continuity. When these considerations are staff, and the FHWA Transportation Engineer, in conflict, the choice is made on the basis as appropriate. Major design features include of judgment of their relative merits. the freeway alignment, geometric cross HIGHWAY DESIGN MANUAL 500-9 May 7, 2012

Figure 502.3

Typical Freeway-to-freeway Interchanges

500-10 HIGHWAY DESIGN MANUAL May 7, 2012

Figure 502.3

Typical Freeway-to-freeway Interchanges (continued) HIGHWAY DESIGN MANUAL 500-11 July 2, 2018 section, geometric design and intersection control of should apply for the first curve after the exit ramp termini, location of separation structures, from a collector-distributor road. The range of closing of local roads, frontage road construction, minimum "DL" (distance) vs. "R" (radius) is bicycle and pedestrian facilities and work on local given in the table in Figure 504.2B. Strong roads. Particularly close involvement should occur consideration should be given to lengthening during preparation of the project initiation document the "DL" distance given in the table when the and project report (see the Project Development subsequent curve is a descending loop or hook Procedures Manual). Such reviews can be ramp, or if the upstream condition is a sustained particularly valuable when exceptions to design downgrade (see AASHTO, A Policy on standards are being considered and alternatives are Geometric Design of Highways and Streets, for being sought. The geometric features of all additional information). interchanges or modifications to existing The exit nose shown on Figure 504.2B may be interchanges must be approved by the Project located downstream of the 23-foot dimension; Delivery Coordinator. however, the maximum paved width between Topic 504 - Interchange Design the mainline and ramp shoulder edges should be 20 feet. Also, see pavement cross slope Standards requirements in Index 504.2(5). 504.1 General Contrasting surface treatment beyond the gore pavement should be provided on both entrance Topic 504 discusses the standards that pertain to both and exit ramps as shown on Figures 504.2A, local service interchanges (various ramp 504.2B, and 504.3K. This treatment can both configurations) and freeway-to-freeway connections. enhance aesthetics and minimize maintenance The design standards, policies and practices covered efforts. It should be designed so that a driver in Indexes 504.2, and 504.5 through 504.8 are will be able to identify and differentiate the typically common to both ramp and connector contrasting surface treatment from the interchange types. Indexes 504.3 and 504.4 pavement areas that are intended for regular or separately discuss ramp standards and freeway-to- occasional vehicular use (e.g., traveled way, freeway connector standards, respectively. shoulders, paved gore, etc.). 504.2 Freeway Entrances and Exits Consult with the District Landscape Architect, (1) Basic Policy. All freeway entrances and exits, District Materials Engineer, and District except for direct connections with median Maintenance Engineer to determine the High-Occupancy Vehicle (HOV) lanes, appropriate contrasting surface treatment of the Express Toll lanes or BRT lanes, shall facility at a specific location. connect to the right of through traffic. Refer to the HOV Guidelines for additional (2) Standard Designs. Design of freeway entrances information specific to direct connections to and exits should conform to the standard HOV lanes. designs illustrated in Figure 504.2A-B (single (3) Location on a Curve. Freeway entrances and lane), and Figure 504.3K (two-lane entrances exits should be located on tangent sections and exits) and/or Figure 504.4 (diverging wherever possible in order to provide maximum branch connections), as appropriate. sight distance and optimum traffic operation. The minimum deceleration length shown on Where curve locations are necessary, the ramp Figure 504.2B shall be provided prior to the entrance and exit tapers should be curved also. first curve beyond the exit nose to assure The radius of the exit taper should be about the adequate distance for vehicles to decelerate same as the freeway edge of traveled way in before entering the curve. The same standard order to develop the same degree of divergence as the standard design (see Figure 504.2C). 500-12 HIGHWAY DESIGN MANUAL March 20, 2020

Figure 504.2A Single Lane Freeway Entrance

HIGHWAY DESIGN MANUAL 500-13 March 20, 2020

Figure 504.2B

Single Lane Freeway Exit

500-14 HIGHWAY DESIGN MANUAL July 2, 2018

On entrance ramps the distance from the inlet Decision sight distance given in Table 201.7 nose (14-foot point) to the end of the should be provided at freeway exits and acceleration lane taper should equal the sum of branch connectors. At secondary exits on the distances shown on Figure 504.2A. The collector-distributor roads, a minimum of 50:1 (longitudinal to lateral) taper may be 600 feet of decision sight distance should be curved to fit the conditions, and the 3,000-foot provided. In all cases, sight distance is radius curve may be adjusted (see Figure 504.2A, measured to the center of ramp lane right of note 3). the nose. When an exit must be located where physical (b) Freeway Entrance--The design speed at the restrictions to visibility cannot be corrected by inlet nose should be consistent with cut widening or object removal, an auxiliary approach alignment standards. If the lane in advance of the exit should be provided. approach is a branch connection or diamond The length of auxiliary lane should be a ramp with high alignment standards, the minimum 600 feet, 1,000 feet preferred. design speed should be at least 50 miles per hour. (4) Design Speed Considerations. In the design of interchanges it is important to provide vertical (c) Ramps--See Index 504.3(1)(a). and horizontal alignment standards which are (d) Freeway-to-Freeway Connections--See consistent with driving conditions expected on Index 504.4(2). branch connections. Sight distance on crest vertical curves should be consistent with (5) Grades. Grades for freeway entrances and exits expected approach speeds. are controlled primarily by the requirements of sight distance. Ramp profile grades should not (a) Freeway Exit--The design speed at the exit exceed 8 percent with the exception of nose should be 50 miles per hour or greater descending entrance ramps and ascending exit for both ramps and branch connections. ramps, where a 1 percent steeper grade is Figure 504.2C allowed. However, the 1 percent steeper grade should be avoided on descending loops to Location of Freeway Ramps minimize overdriving of the ramp (see Index on a Curve 504.3 (8)). Profile grade considerations are of particular concern through entrance and exit gore areas. In some instances the profile of the ramp or connector, or a combination of profile and cross slope, is sufficiently different than that of the freeway through lanes that grade breaks across the gore may become necessary. Where adjacent lanes or lanes and paved gore areas at freeway entrances and exits are not in the same plane, the algebraic difference in pavement cross slope should not exceed 5 percent (see Index 301.3). The paved gore area is typically that area between the diverging or converging edge of traveled ways and the 23-foot point. In addition to the effects of terrain, grade lines are also controlled by structure clearances (see Indexes 204.6 and 309.2). Grade lines for overcrossing and undercrossing roadways HIGHWAY DESIGN MANUAL 500-15 March 20, 2020

should conform to the requirements of HDM not prohibited, provisions need to be made at Topic 104 Roads Under Other Jurisdictions. interchanges to accommodate bicyclists and pedestrians. See Topic 116 and the California (a) Freeway Exits--Vertical curves located just MUTCD for additional guidance. beyond the exit nose should be designed with a minimum 50 miles per hour stopping 504.3 Ramps sight distance. Beyond this point, progressively lower design speeds may be (1) General. used to accommodate loop ramps and other (a) Design Speed--When ramps terminate at an geometric features. intersection at which all traffic is expected to make a turning movement, the minimum Ascending off-ramps should join the design speed along the ramp should be crossroads on a reasonably flat grade to 25 miles per hour. When a “through” expedite truck starts from a stopped movement is provided at the ramp terminus, condition. If the ramp ends in a crest the minimum ramp design speed should vertical curve, the last 50 feet of the ramp should be on a 5 percent grade or less. meet or exceed the design speed of the highway facility for which the through There may be cases where a drainage movement is provided. The design speed feature is necessary to prevent crossroads along the ramp will vary depending on water from draining onto the ramp. alignment and controls at each end of the On descending off-ramps, the sag vertical ramp. An acceptable approach is to set curve at the ramp terminal should be a design speeds of 25 miles per hour and minimum of 100 feet in length. 50 miles per hour at the ramp terminus and (b) Freeway Entrances--Entrance profiles exit nose, respectively, the appropriate should approximately parallel the profile of design speed for any intermediate point on the freeway for at least 100 feet prior to the the ramp is then based on its location inlet nose to provide intervisibility in relative to those two points. When short merging situations. The vertical curve at radius curves with relatively lower design the inlet nose should be consistent with speeds are used, the vertical sight distance approach alignment standards. should be consistent with approach vehicle speeds. See Index 504.2(4) for additional Where truck volumes (three-axle or more) information regarding design speed for exceed 20 vehicles per hour on ascending ramps. entrance ramps to freeways and expressways with sustained upgrades (b) Lane Width--Ramp lanes shall be a exceeding 2 percent, a 1,500-foot length of minimum of 12 feet in width. Where auxiliary lane should be provided in order to ramps have curve radii of 350 feet or less, ensure satisfactory operating conditions. measured along the outside edge of Additional length may be warranted based traveled way for single lane ramps or on the thorough analysis of the site specific along the outside lane line for multilane grades, traffic volumes, and calculated ramps, with a central angle greater than speeds; and after consultation with the 60 degrees, the single ramp lane, or the District Traffic Safety Engineer or designee lane furthest to the right if the ramp is and the Project Delivery Coordinator or multilane, shall be widened in District Design Liaison. Also, see accordance with Table 504.3 in order to Index 204.5 "Sustained Grades". accommodate large truck wheel paths. See Topic 404. Consideration may be given (6) Bus Stops. See Index 108.2 and 303.4 for to widening more than one lane on a general information. multilane ramp with short radius curves if (7) Bicycle and Pedestrian Conditions. On there is a likelihood of considerable transit freeways where bicycle or pedestrian travel is or truck usage of that lane. 500-16 HIGHWAY DESIGN MANUAL March 20, 2020

Table 504.3 any project that proposes additional capacity, Ramp Widening for Trucks modification of an existing interchange, or construction of a new interchange, within the Ramp Radius Widening Lane Width freeway corridors identified in the Ramp (ft) (ft) (ft) Metering Development Plan (RMDP), regardless of funding source. Projects designed <150 8 20 for new or existing freeway segments 150 – 179 5 17 experiencing recurring traffic congestion and/or 180 – 209 4 16 a high frequency of vehicle collisions may 210 – 249 3 15 include provisions for entrance ramp metering, 250 – 299 2 14 whether or not the freeway segment locations -300 – 350 1 13 are listed in the RMDP. >350 0 12 All geometric designs for ramp metering installations must be discussed with the Project (c) Shoulder Width--Shoulder widths for Delivery Coordinator or District Design ramps shall be as indicated in Table Liaison. Design features or elements which 302.1. Typical ramp shoulder widths are deviate from design standards require the 4 feet on the left and 8 feet on the right. approvals described in Index 82.2. (d) Lane Drops--Typically, lane drops are to be See the RMDM for ramp metering guidance, accomplished over a distance equal to WV. procedures, and policies to be used in Where ramps are metered, the conjunction with the guidance in this manual. recommended lane drop taper past the meter Where traffic-related ramp metering guidance is limit line is 50 to 1 (longitudinal to lateral). noted in this Chapter, reference is made to the Depending on approach geometry and RMDM for exception instructions and further speed, the lane drop transition between the information. limit line and the 6-foot separation point should be accomplished with a taper of Geometric ramp design for operational between 30:1 and 50:1 (longitudinal to improvement projects which include ramp lateral). This is further explained in Index metering should be based on current peak-hour 504.3(2)(b) for metered multilane entrance traffic volume. If this current data is not ramps. However, the lane drop taper past available it should be obtained before the limit line shall not be less than 15 to proceeding with design. Peak hour traffic data 1. from the annual Caltrans Traffic Volumes book is not adequate for this application. Lane drop tapers should not extend beyond the 6-foot point without the provision of an The design advice and typical designs that auxiliary lane. follow should not be directly applied to ramp meter installation projects, especially retrofit (e) Lane Additions -- Lane additions to ramps designs. Every effort should be made by the are usually accomplished by use of a designer to exceed the recommended minimum 120-foot bay taper. See Table 405.2A for standards provided herein, where conditions are the geometrics of bay tapers. not restrictive. (2) Ramp Metering (a) Metered Freeway Entrance Ramps Caltrans Deputy Directive (DD) No. 35-R1, (1 General Purpose (GP) + 1 HOV Ramp Metering, contains the statewide policy Preferential Lane) for ramp metering which delegates According to the RMDM, a High- responsibility for its implementation in part Occupancy Vehicle (HOV) preferential through the Ramp Metering Design Manual lane shall be provided where ramp meters (RMDM). DD 35-R1 specifies that provisions are installed, and each HOV preferential for entrance ramp metering shall be included in HIGHWAY DESIGN MANUAL 500-17 July 2, 2018

lane should be metered. See the RMDM for preferential lane, see Figures 504.3C and exception procedures from the Ramp 504.3D. In restrictive conditions, a Metering policy. See Figures 504.3A and minimum 500-foot auxiliary lane should be 504.3B for typical freeway entrance ramp provided beyond the ramp convergence metering (1 GP Lane + 1 HOV Preferential point when truck volumes (3-axle or more) Lane). are 5 percent or greater on ascending entrance ramps to freeways with sustained Due to the operational benefits of an upgrades exceeding 3 percent (i.e., at least auxiliary lane, the merge from the metered throughout the merge area). entrance ramp to the freeway should include an auxiliary lane with a minimum length of In general, the vehicle occupancy 300 feet beyond the ramp convergence requirement for ramp meter HOV point. See Figure 504.3A. preferential lanes is typically two or more persons per vehicle. At some locations, a Where truck volumes (3-axle or more) are higher vehicle occupancy requirement may 5 percent or greater on ascending entrance be necessary. The occupancy requirement ramps to freeways with sustained upgrades should be based on the HOV demand and exceeding 3 percent (i.e., at least should match with other HOV facilities in throughout the merge area), a minimum the vicinity. 1000-foot length of auxiliary lane should be provided beyond the ramp convergence A HOV preferential lane should typically be point. placed on the left; however, demand and operational characteristics at the ramp When ramp volumes exceed 1,500 vph, a entrance may dictate otherwise. Design of 1,000-foot minimum length of auxiliary the HOV preferential lane at a metered lane should be provided beyond the ramp entrance ramp requires the review and convergence point. If an auxiliary lane is concurrence of the Caltrans District Traffic included, the ramp lane transition may be Operations Branch responsible for ramp extended to the convergence point. metering. However, the proximity of the nearest interchange may warrant weaving analysis Access to the HOV preferential lane may be to determine the acceptability of extending provided in a variety of ways depending on the ramp lane transition beyond the 6-foot interchange type and available storage separation point. A longer auxiliary lane length for queued vehicles. Where queued should be considered where mainline/ramp vehicles in the general purpose (GP) lane gradients and truck volumes warrant may block access to the HOV preferential additional length. lane, consider providing direct or separate access. To avoid trapping GP traffic in an (b) HOV Preferential Lane HOV preferential lane, the signing and Ramp meter installations should operate in pavement marking at the ramp entrance conjunction with, and complement other should direct motorists into the GP lane(s). transportation management system See the RMDM, Chapter 3 for signing and elements and transportation modes. As pavement markings. Designs should such, ramp meter installations should consider pedestrian/bicycle volumes, include preferential treatment of carpools especially when the entrance ramp is and transit riders. Specific treatment(s) located near a school or the local highway must be tailored to the unique conditions at facility includes a designated bicycle lane or each ramp location. route. See Index 403.6 for right-turn-only Where restrictive conditions, vehicle lane guidance where bicycle travel is volumes less than 500 vehicles per hour permitted. Contact the District Traffic (vph), or other engineering judgement exist Safety Engineer or designee and the Project in support of an exception to the HOV Delivery Coordinator or District Design 500-18 HIGHWAY DESIGN MANUAL December 16, 2016

Figure 504.3A Typical Freeway Entrance Loop Ramp Metering (1 GP Lane + 1 HOV Preferential Lane)

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Figure 504.3B Typical Successive Freeway Entrance Ramp Metering (1 GP Lane + 1 HOV Preferential Lane)

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Figure 504.3C Restrictive Condition Freeway Entrance Ramp Metering (1 GP Lane)

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Figure 504.3D Restrictive Condition Freeway Entrance Loop Ramp Metering (1 GP Lane)

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Liaison to discuss the application of traffic along urban and suburban freeway specific design and/or general issues corridors. The adverse effects of bus and related to the design of HOV preferential truck traffic on the operation of these lane access. ramps (i.e., off-tracking, sight restriction, acceleration characteristics on upgrades, Signing for a HOV preferential lane should etc.) is minimized when the ramp be placed to clearly indicate which lane is alignment is tangential or consists of curve designated for HOVs. Real-time signing at radii not less 300 feet. Proposed three-lane the ramp entrance, such as an overhead loop and four-lane entrance ramps require changeable message sign, may be the review and approval by the Deputy necessary at some locations if pavement District Director of Traffic Operations. delineation and normal signing do not provide drivers with adequate lane usage On multi-lane entrance ramps, the multi- information. To avoid leading Single- lane segment should transition to a single Occupancy Vehicles (SOV) into a HOV lane width between the ramp meter limit preferential lane, pavement delineation at line and the 6-foot separation point (from the ramp entrance should lead drivers into the mainline edge of traveled way). the SOV lane. The lane drop transition should be (c) Metered Multilane Freeway Entrance accomplished with a taper of 50:1 Ramps (longitudinal to lateral) unless a lesser taper is warranted by site and/or project The number of metered lanes at an entrance specific conditions which control the ramp ramp is the number of both metered general geometry and/or anticipated maximum purpose (GP) and high-occupancy vehicle speed of ramp traffic. For example, "loop" (HOV) preferential lanes at the limit line. entrance ramps would normally not allow The minimum number of metered GP lanes traffic to attain speeds which would is determined based on GP traffic demand. warrant a 50:1 (longitudinal to lateral) lane The number of metered HOV preferential drop taper. Also, in retrofit situations, lanes is determined based on HOV demand existing physical, environmental or right of using the same guidelines as GP traffic way constraints may make it impractical to demand, as well as the HOV preferential provide a 50:1 taper, especially if the lane policy. maximum anticipated approach speed will A multilane ramp segment may be be less than 50 miles per hour. Therefore, provided to increase vehicle storage within depending on approach geometry and the available ramp length. At on-ramps speed, the lane drop transition between the with peak hour volume between 500 and limit line and the 6-foot separation point 900, a two-lane ramp meter may be should be accomplished with a taper of provided to double the vehicles stored between 30:1 and 50:1 (longitudinal to within the available storage area. See lateral). However, the lane drop taper RMDM for additional multilane freeway past the limit line shall not be less than entrance ramp guidance. 15 to 1. Figures 504.3E and 504.3F illustrate The merge from the metered entrance ramp typical designs for metered multilane to the freeway should include a 300-foot diagonal and loop freeway entrance ramps. minimum auxiliary lane beyond the ramp On multilane loop ramps, typically only the convergence point. right lane needs to be widened to Where truck volumes (3-axle or more) are accommodate design vehicle off-tracking. 5 percent or greater on ascending entrance See Index 504.3(1)(b). ramps to freeways with sustained upgrades Three-lane metered ramps are typically exceeding 3 percent (i.e. at least needed to serve peak (i.e., commute) hour HIGHWAY DESIGN MANUAL 500-23 December 16, 2016

Figure 504.3E Typical Multilane Freeway Diagonal Entrance Ramp Metering (2 GP Lanes + 1 HOV Preferential Lane)

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Figure 504.3F Typical Multilane Freeway Loop Entrance Ramp Metering (2 GP Lanes + 1 HOV Preferential Lane)

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throughout the merge area), a minimum See RMDM Section 1.11 for additional 1,000 feet length of auxiliary lane should metered freeway-to-freeway connector be provided beyond the ramp convergence guidance. point. AASHTO, A Policy on Geometric (e) Queue Storage Length Design of Highways and Streets, provides additional guidance on acceleration lane In order to maximize the effectiveness of length on grades. operational strategies, an important design consideration for a ramp meter system is When ramp volumes exceed 1,500 vph, a providing adequate storage for queues. 1,000-foot minimum length of auxiliary Storage length design requires the review lane should be provided beyond the ramp and concurrence of the Caltrans District convergence point. If an auxiliary lane is Traffic Operations Branch responsible for included, the ramp lane transition may be ramp metering. See RMDM Section 1.4 extended to the convergence point. for detailed queue storage length design However, the proximity of the nearest guidance. interchange may warrant weaving analysis to determine the acceptability of extending To minimize the impact on local street the ramp lane transition beyond the 6-foot operation, every effort should be made to separation point. A longer auxiliary lane meet the recommended storage length. should be considered where mainline/ramp Wherever feasible, ramp metering storage gradients and truck volumes warrant should be contained on the ramp by either additional length. widening or lengthening it. Improvements to the local street system in the vicinity of (d) Metered Freeway-to-Freeway Connectors the ramp should also be thoroughly Freeway-to-freeway connectors may also investigated where there is insufficient be metered. The need to meter a freeway- storage length on the ramp and the ramp to-freeway connector should be queue will adversely affect local street determined on an individual basis. operation. Note that excessive queue Because connector ramps provide a link length may also impact the mobility of between two high speed facilities, drivers pedestrians and bicyclists. The storage do not expect to stop, nor do they expect to length that can be provided on the ramp approach a stopped vehicle. may be limited by the weaving distance to the next off-ramp and/or available right of The installation of ramp meters on way. Local street improvements can connector ramps shall be limited to include widening or restriping the street(s) those facilities which meet or exceed the or intersection(s) to provide additional following geometric design criteria: storage or capacity. Signal timing • Standard lane and shoulder widths. revisions along the corridor feeding the ramp can also enhance the storage • "Tail light" sight distance, capability. These will require coordination measured from a 3 ½ feet eye height with the local agency consistent with the to a 2-foot object height, is provided regional traffic operations strategy. for a design speed of 50 miles per hour minimum. It is the responsibility of the Department, on Department initiated projects, to All lane drops on connectors should be mitigate the effect of ramp metering, for accomplished over a distance not less than initial as well as future operational impacts, WV. All lane drop transitions on to local streets that lead to metered freeway connectors shall be accomplished with a entrance ramps. It is the responsibility of taper of 50:1 (longitudinal to lateral) developers and/or local agencies, to minimum, (see Figures 504.3G and mitigate any impact to existing ramp meter 504.3H). facilities, future ramp meter installations, 500-26 HIGHWAY DESIGN MANUAL November 20, 2017

Figure 504.3G Typical Freeway-to-Freeway Connector Ramp Metering (1 GP Lane + 1 HOV Preferential Lane)

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Figure 504.3H Typical Freeway-to-Freeway Connector Ramp Metering (2 GP Lanes + 1 HOV Preferential Lane)

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or local streets, when those impacts are (j) Enforcement Areas and Maintenance attributable to new development and/or Pullouts local agency roadway improvement Division of Traffic Operations policy projects. requires a paved enforcement area to be (f) Pavement Structure provided on all projects that include new or reconstructed metered entrance ramps or In planning for the possibility of future connectors. widening, the pavement structure for the ramp shoulders should be equal to the ramp See the RMDM for exception procedures traveled way pavement structure. In to this policy. locations where failure of loop detectors Enforcement areas are used by the due to flexible pavement deterioration is a California Highway Patrol (CHP) to concern, a Portland Cement Concrete enforce minimum vehicle occupancy (PCC) pad may be considered on new requirements. The paved enforcement area construction and rehabilitation projects. should be placed on the right side of a The concrete pad should cover the metered entrance ramp, downstream of the metering detector loop area upstream and metering signals, and as close to the limit downstream of the limit line. line as practical to facilitate CHP (g) Meter Signal Location enforcement. See Figures 504.3A to 504.3H for the typical layout and For the location of ramp meter signal dimensions of enforcement areas. standards, see the RMDM, Chapter 2. The District Traffic Operations Branch (h) Limit Line Location responsible for ramp metering must The limit line location will be determined coordinate enforcement issues with the by the selected transition taper, but should CHP. The CHP Area Commander must be be a minimum of 75 feet upstream of the contacted during the development of the 23-foot separation point. See the RMDM project report or PA & ED phase, prior to Section 1.7 for additional guidance. design, to discuss any variations needed to (i) Modifications to Existing HOV the CHP enforcement area designs shown in this manual. Variations to enforcement Preferential Lanes area dimensions or location require the Changes in traffic conditions, proposals for review and concurrence of the CHP and the interchange modifications, recurrent Caltrans District Traffic Operations operational problems affecting the local Branch responsible for ramp metering. facility, or the need to further improve mainline operations through more Division of Traffic Operations policy restrictive metering are opportunities to requires a paved Maintenance Vehicle reevaluate the need for a HOV preferential Pullout (MVP) to be provided at a location lane. Typically, an existing HOV for maintenance and operations personnel preferential lane may be considered for to access controller cabinets. The MVP conversion to a GP lane if the existing should be placed upstream or next to HOV preferential lane is underutilized, controller cabinets. The MVP and the there is a need for additional queue storage controller cabinets should be placed on the for the GP lanes, or an alternate entrance same side of the entrance ramp. At loop ramp HOV preferential lane is available entrance ramps, locate the MVP to the within 1½ miles. See the RMDM for inside of the loop ramp. A paved walkway procedures when considering conversion should be provided between the MVP and of a HOV preferential lane to a GP lane at the controller cabinets. See RMDM a metered entrance ramp. Section 2.4 for controller cabinet placement. See Topic 309, Clearances, for HIGHWAY DESIGN MANUAL 500-29 December 14, 2018

placement guidance of fixed objects such • Vehicles turning left onto an on-ramp are as controller cabinets. Refer to HDM to be prevented, to the maximum extent Index 107.2 and the Standard Plans for the feasible, from turning prematurely onto the layout and pavement structure section off-ramp by placing or extending a curbed details of an MVP. See the RMDM for median on the crossroad to physically exception procedures to this policy. discourage this move. Attention needs to (3) Location and Design of Ramp Intersections on be given to accommodating truck turn the Crossroads. templates for design vehicles entering and exiting the freeway. See Index 404.5 for Factors which influence the location of ramp further turning template guidance. Truck intersections on the crossroads include sight aprons could be provided if the size of an distance, construction and right of way costs, intersections becomes too large for an bicycle and pedestrian mobility, circuitous occasional truck. See Index 405.10, travel for left-turn movements, crossroads Roundabouts, and the references therein gradient at ramp intersections, storage for design guidance on truck aprons. requirements for left-turn movements off the crossroads, and the proximity of other local Isolated off-ramps are to be avoided to road or bicycle path intersections. minimize the potential for wrong-way movements. If the isolated off-ramp is Ramp intersections with local roads are necessary, the leading curb return from the intersections at grade. Chapter 400 and the perspective of a vehicle on the crossroad references therein contain general guidance. approaching from the same side as the off-ramp For ramp intersections, a wrong-way is made with a short radius curve of 3 to 5 feet. movement onto an off-ramp can have severe State or local roads and driveways opposite consequences. The California MUTCD also isolated off-ramps are to be avoided as there is contains guidance for signing and striping to no corresponding on-ramp for cross traffic to deter wrong-way movements. take. See this chapter for further interchange Interchange Types L-7, L-8, and L-9 are partial and ramp guidance. cloverleaf designs with ramps at a right angle Ramp terminals should connect where the to the crossroad where the off-ramps and on- grade of the overcrossing is 4 percent or less to ramps are adjacent to each other on the same avoid potential overturning of trucks. side of the crossroad that offer benefits for non- motorized travel modes; however, additional For left-turn maneuvers from an off-ramp at an design considerations as follows may be unsignalized intersection, the length of appropriate in order to deter wrong-way crossroads open to view should be according to movements: the corner sight distance criteria in Index 405.1. When proposing uncontrolled entries and exits • The entrance and exit ramps should be from freeway ramps with local roads, see the clearly visible from the crossroad. Design of Intersections at Interchanges Concrete barrier or guardrail placed guidance in Index 403.6(2). between the ramps can block the view from the crossroad. If feasible, the concrete Corner sight distance restrictions may be barrier or guardrail channelization feature caused by bridge railings, bridge piers, or should be set back from the crossroad edge slopes. Corner sight distance is measured of shoulder 20 to 50 feet with a raised along the crossroad between the vehicle in the traffic island placed from the ramp termini center of the outside lane of the crossroad to the begin point of the separation feature. approaching the ramp and the eye of the driver See Index 405.4 for further traffic island of the ramp vehicle that is set back from the guidance. Consult the District Traffic edge of traveled way of the crossroad. Safety Branch for available options. 500-30 HIGHWAY DESIGN MANUAL December 14, 2018

Figure 504.3I illustrates the relationship of the Index 202.2 use the 12 percent emax rate ramp vehicle that is set back from an except where snow and ice conditions prevail. overcrossing structure, which is based on the In restrictive cases where the length of curve is sight distance controlled by the bridge rail too short to develop standard superelevation, location using the corner sight distance criteria. the highest obtainable rate should be used (see The same relationship exists for sight distance Index 202.5). If feasible, the curve radius can controlled by bridge piers or slopes. be increased to reduce the standard Where the clear sight triangle is unobtainable superelevation rate. Both edge of traveled way according to Index 405.1, sight distance should and edge of shoulder should be examined at be provided by flaring the end of the ramp junctions to assure a smooth transition. overcrossing structures or setting back the piers Under certain restrictive conditions the or end slopes of an undercrossing structure. standard superelevation rate discussed above The sight line should take into account if the may not be required on the curve nearest the bridge railing is see-through or is at a height ramp intersection of a ramp. The specific below the driver’s eye height. Note, the bridge conditions under which lower superelevation railing may have added features, such as chain rates would be considered must be evaluated on link railing, tubular hand railing, sound barrier, a case-by-case basis and must be discussed decorative architectural pedestals, etc. with the Project Delivery Coordinator or the If signals are warranted within 5 years of District Design Liaison and then documented construction, consideration may be given to as required by the Project Delivery installing signals according to Part 4 of the Coordinator. California MUTCD, 4B.107(CA) and 4C.09. (5) Single-lane Ramps. Single lane ramps are For additional information on sight distance those ramps that either enter into or exit from requirements at signalized intersections, see the freeway as a single lane. These ramps are Index 405.1. often widened near the ramp intersection with the crossroads to accommodate turning The minimum distance (curb return to curb movements onto or from the ramp. When return) between ramp intersections and additional lanes are provided near an entrance local road intersections shall be 400 feet. ramp intersection, the lane drop should be The preferred minimum distance should be accomplished over a distance equal to WV. 500 feet. This does not apply to Resurfacing, The lane to be dropped should be on the right Restoration and Rehabilitation (3R), ramp so that traffic merges left. widening, restriping or other projects which do not reconfigure the interchange. This standard Exit ramps in metropolitan areas may require does apply to projects proposing to realign a multiple lanes at the intersection with the local street. crossroads to provide additional storage and capacity. If the length of a single lane ramp Where intersections are closely spaced, traffic exceeds 1,000 feet, an additional lane should operations are often inhibited by short weave be provided on the ramp to permit passing distance, storage lengths, and signal phasing. maneuvers. Figure 504.3J illustrates In addition it is difficult to provide proper alternative ways of transitioning a single lane signing and delineation. The District Traffic exit ramp to two lanes. The decision to use Branch should be consulted regarding traffic Alternate A or Alternate B is generally based engineering studies needed to determine the on providing the additional lane for the minor appropriate signage, delineation, and form of movement. intersection control. (6) Two-lane Exit Ramps. Where design year (4) Superelevation for Ramps. The factors estimated volumes exceed 1500 equivalent controlling superelevation rates discussed in passenger cars per hour, a 2-lane ramp should Topic 202 apply also to ramps. As indicated in be provided. Provisions should be made for HIGHWAY DESIGN MANUAL 500-31 December 14, 2018

Figure 504.3I Location of Ramp Intersections on the Crossroads

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possible widening to three or more lanes at the driver efforts to maintain speed on entrance crossroads intersection. Figure 504.3K ramps to facilitate acceleration and merging. illustrates the standard design for a 2-lane exit. Where the loop is of short radius and is also on An auxiliary lane approximately 1,300 feet a steep descent (over 6 percent), it is important long should be provided in advance of a 2-lane to develop the standard 2/3 full superelevation exit. For volumes less than 1500 but more than rate by the beginning of the curve (see 900, a one-lane width exit ramp should be Index 504.2(5)). When accommodating design provided with provision for adding an auxiliary vehicles in Rural Developing Corridors that are lane and an additional lane on the ramp. largely composed of industrial, commercial or retail buildings located separately from (7) Two-lane Entrance Ramps. These ramps are housing, the following considerations may be discouraged in congested corridors. Early necessary to meet the standard 2/3 full discussion with the Project Delivery superelevation rate on loop entrance ramps: Coordinator, District Design Liaison and the District Traffic Engineer or designee is • Begin the ramp with a short tangent recommended whenever two-lane entrance (75 feet to 100 feet) that diverges from the ramps are being considered. cross street at an angle of 4 to 9 degrees. (8) Loop Ramps. Normally, loop ramps should • Provide additional tangent length as site have one lane and shoulders unless a second conditions allow. lane is needed for capacity or ramp metering purposes. Consideration should be given to The Angle of Intersection guidance in providing a directional ramp when loop Index 403.3 applies to all on-ramps including volumes exceed 1500 vehicles per hour. If two loops. lanes are provided, normally only the right lane (9) Distance Between Successive On-ramps. The needs to be widened for trucks. See Topic 404 minimum distance between two successive on- for additional discussion on lane widths and ramps to a freeway lane should be the distance design of ramp intersections to accommodate needed to provide the standard on-ramp the design vehicle. See Index 504.3(1) for a acceleration taper shown on Figure 504.2A. discussion regarding on-ramp widening for This distance should be about 1,000 feet unless trucks. the upstream ramp adds an auxiliary lane in Radii for loop ramps should normally range which case the downstream ramp should merge from 150 feet to 200 feet. Increasing the radii with the auxiliary lane in a standard 50:1 beyond 200 feet is typically not cost effective (longitudinal to lateral) convergence. The as the slight increase in design speed is usually distance between on-ramp noses will then be outweighed by the increased right of way controlled by interchange geometry. requirements and the increased travel distance. (10) Distance Between Successive Exits. The Curve radii of less than 120 feet should also be minimum distance between successive exit avoided. Extremely tight curves lead to ramps for guide signing should be 1,000 feet on increased off-tracking by trucks and increase the freeway and 600 feet on collector- the potential for vehicles to enter the curve with distributor roads. excessive speed. Therefore, consider providing (11) Curbs. Curbs should not be used on ramps the ramp lane pavement structure on shoulders except in the following locations: for curves with a radius less than 300 feet (see Indexes 626.1 and 636.1). (a) A Type D curb or 4-inch Type B curb (see Index 303.2) may be used on both sides of Of particular concern in the design of loop the separation between freeway lanes and a ramps are the constraints imposed on large trucks. Research indicates that trucks often parallel collector-distributor road. enter loops with excessive speed, either due to (b) A B4 curb may be used as shown in inadequate deceleration on exit ramps or due to Figure 504.2A to control drainage or where HIGHWAY DESIGN MANUAL 500-33 December 16, 2016

Figure 504.3J Transition to Two-lane Exit Ramp

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Figure 504.3K Two-Lane Connectors and Entrance/Exit Ramps

HIGHWAY DESIGN MANUAL 500-35 July 2, 2018

the gore cross slope would be greater than needed to obtain increased stopping sight allowed in Index 504.2(5). When the distance for higher design speeds. optional B4 curb is used at the entrance (4) Shoulder Width. ramp inlet nose, the shoulder adjacent to the curb should be the same width as the (a) Single-lane and Two-lane Connections-- ramp shoulder approaching the curb. The The width of shoulders on single-lane B4 gutter pan can be included as part of the and two-lane (except as described shoulder width. As stated in Index below) freeway-to-freeway connectors 405.4(2), curbs are typically discouraged shall be 5 feet on the left and 10 feet on where posted speeds are over 40 miles per the right. A single lane freeway-to- hour. Curbs at gore areas must be freeway connector that has been determined on a case-by-case basis. widened to two lanes solely to provide passing opportunities and not due to (c) Curbs may be used where necessary at the capacity requirements shall have a ramp connection with the local street for 5-foot left shoulder and at least a 5-foot the protection of pedestrians, for right shoulder (see Index 504.4(5)). channelization, and to provide compatibility with the local facility. (b) Three-lane Connections--The width of shoulders on three-lane connectors shall (d) The Type E curb may be used only in be 10 feet on both the left and right sides. special drainage situations, for example, where drainage parallels and flows against (5) Single-lane Connections. Freeway-to-freeway the face of a retaining wall. connectors may be single lane or multilane. Where design year volume is between 900 and In general, curbs should not be used on the high 1500 equivalent passenger cars per hour, initial side of ramps or in off-ramp gore areas except construction should provide a single lane at collector-distributor roads. The off-tracking connection with the capability of adding an of trucks should be analyzed when considering additional lane. Single lane directional curbs on ramps. connectors should be designed using the (12) Dikes. Dikes may be used where necessary to general configurations shown on control drainage. For additional information Figure 504.2A and 504.2B, but utilizing the see Index 303.3. flatter divergence angle shown in Figure 504.4. Single lane loop connectors may use a diverge 504.4 Freeway-to-Freeway Connections angle of as much as that shown on (1) General. All of the design criteria discussed in Figure 504.2B for ramps, if necessary. The Indexes 501.3, 504.2 and 504.3 apply to choice will depend upon interchange freeway to freeway connectors, except as configuration and driver expectancy. Single discussed or modified below. lane connectors in excess of 1,000 feet in length should be widened to two lanes to (2) Design Speed. The design speed for single lane provide for passing maneuvers (see directional and all branch connections should Index 504.4(4)). be a minimum of 50 miles per hour. When smaller radius curves, with lower design (6) Branch Connections. A branch connection is speeds, are used the vertical sight distance defined as a multilane connection between two should be consistent with approaching vehicle freeways. A branch connection should be speeds. Design speed for loop connectors provided when the design year volume exceeds should be consistent with the radii guidance 1500 equivalent passenger cars per hour. discussed in Index 504.3(8). Merging branch connections should be (3) Grades. The maximum profile grade on designed as shown in Figure 504.3K. freeway-to-freeway connections should not Diverging branch connections should be exceed 6 percent. Flatter grades and longer designed as shown in Figure 504.4. The vertical curves than those used on ramps are diverging branch connection leaves the main 500-36 HIGHWAY DESIGN MANUAL March 20, 2020

freeway lanes on a flatter angle shown in volumes are high, the need for an auxiliary lane Figure 504.4 than the standard 2-lane ramp exit between the interchanges should be determined in connection shown in Figure 504.3K. The accordance with Index 504.7. standard ramp exit connects to a local street. Auxiliary lanes may be used for the orientation of The diverging branch connection connects to traffic at 2-lane ramps or branch connections as another freeway and has a flatter angle that illustrated on Figure 504.3K and Figure 504.4. The allows a higher departure speed. length and number of auxiliary lanes in advance of At a branch merge, a 2,500-foot length of 2-lane exits are based on percentages of turning auxiliary lane should be provided beyond the traffic and a weaving analysis. merge of one lane of the inlet, except where it Auxiliary lanes should be considered on all freeway does not appear that capacity on the freeway entrance ramps with significant truck volumes. The will be reached until five or more years after grade, volumes and speeds should be analyzed to the 20 year design period. In this case the determine the need for auxiliary lanes. An auxiliary length of auxiliary lane should be a minimum lane would allow entrance ramp traffic to accelerate of 1,000 feet. For diverging connections where to a higher speed before merging with mainline less than capacity conditions beyond the design traffic, or simply provide more opportunity to year are anticipated, the length of auxiliary lane merge. See Index 504.2 for specific requirements. in advance of the exit should be 1,300 feet. (7) Lane Drops. The lane drop taper on a freeway- 504.6 Mainline Lane Reduction at to-freeway connector should not be less than Interchanges WV. The basic number of mainline lanes should not be (8) Metering. Any decision to meter freeway-to- dropped through a local service interchange. The freeway connectors must be carefully same standard should also be applied to freeway-to- considered as driver expectancy on these types freeway interchanges where less than 35 percent of of facilities is for high-speed uninterrupted the traffic is turning (see Figure 504.4). Where more flow. If metering is anticipated on a connector, than 35 percent of the freeway traffic is turning, discussions with the Project Delivery consideration may be given to reducing the number Coordinator and the District Traffic Engineer of lanes. No decision to reduce the number of lanes or designee should take place as early as should be made without the approval of the District possible. Issues of particular concern are Traffic Operations Unit. Additionally, adequate adequate deceleration lengths to the end of the structure clearance (both horizontal and vertical) queue, potential need to widen shoulders if should be provided to accommodate future sight distance is restricted (particularly on- construction of the dropped lane if required. ramps with 5-foot shoulders on each side), and Where the reduction in traffic volumes is sufficient the potential for queuing back onto the to warrant a decrease in the basic number of lanes, a freeway. preferred location for the lane drop is beyond the 504.5 Auxiliary Lanes influence of an interchange and preferably at least one-half mile from the nearest exit or inlet nose. It In order to ensure satisfactory operating conditions, is desirable to drop the right lane on tangent auxiliary lanes may be added to the basic width of alignment with a straight or sag profile so vehicles traveled way. can merge left with good visibility to the pavement Where an entrance ramp of one interchange is markings in the merge area (see Index 201.7). closely followed by an exit ramp of another 504.7 Weaving Sections interchange, the acceleration and deceleration lanes should be joined with an auxiliary lane. Auxiliary A weaving section is a length of one-way roadway lanes are frequently used when the entrance ramp- where vehicles are crossing paths, changing lanes, to-exit ramp spacing, measured as shown in or merging with through traffic as they enter or exit Figure 504.2A, is less than 2,000 feet. Where a freeway or collector-distributer road. interchanges are more widely spaced and ramp HIGHWAY DESIGN MANUAL 500-37 May 7, 2012

Figure 504.4 Diverging Branch Connections 500-38 HIGHWAY DESIGN MANUAL March 20, 2020

A single weaving section has an inlet at the upstream highways. Other methods, such as the one contained end and an exit at the downstream end. A multiple in the 1994 HCM, may not always produce accurate weaving section is characterized by more than one results. point of entry followed by one or more points of exit. The criteria contained within this Index apply to: A rough approximation for adequate length of a • New interchanges. weaving section is one foot of length per weaving vehicle per hour. This rate will approximately • Modifications to existing interchanges including provide a Level of Service (LOS) C. access control revisions for new ramps or the There are various methods for analyzing weaving relocation/elimination of existing ramps. sections. Two methods which provide valid results • Projects to increase mainline capacity when are described below. existing interchanges do not meet interchange The Leisch method, which is usually considered the spacing requirements. easiest to use, is illustrated in Figure 504.7A. This Weaving sections in urban areas should be designed method was developed by Jack Leisch & Associates for LOS C or D. Weaving sections in rural areas and may be used to determine the length of weaving should be designed for LOS B or C. Design rates for sections for both freeways and collector-distributor lane balanced weaving sections where at least one roads. The Leisch weaving charts determine the ramp or connector will be two lanes should not result level of service for the weaving volumes for the in a LOS lower than the middle of LOS D using length of the weaving section from the first panel on Figure 504.7A. Mainline through capacity is the lower left of the chart. The analysis is dependent optimized when weaving movements operate at on whether the section is balanced or unbalanced, as least one level of service better than the mainline defined in Figure 504.7B. The level of service for level of service. In determining acceptable hourly the total volume over all lanes of the weaving operating volumes, peak hour factors should be section is then found from the panels on the right of used. the chart. The weaving chart should not be extrapo- lated. Between interchanges, the minimum entrance ramp-to-exit ramp spacing, measured as shown Pages 234-238 of the 1965 Highway Capacity on Figures 504.2A and 504.2B shall be 2,000 feet Manual (HCM) provide a method for determining in urban areas, 5,000 feet outside urban areas, the adequacy of weaving sections near single lane and 5,000 feet between freeway-to-freeway ramps. It is often referred to as the LOS D method. interchanges and other interchanges. The This method is also documented in Traffic Bulletin volumes used must be volumes unconstrained by 4 which is available from the District Division of metering regardless of whether metering will be Traffic Operations. The LOS D method can be used used. It should be noted that a weaving analysis to project volumes along a weaving section. These must be considered over an entire freeway segment volumes can be compared to the capacities along the as weaving can be affected by other nearby ramps. same weaving section. The District Traffic Operations Branch should be Volumes in passenger car equivalents per hour consulted for difficult weaving analysis problems. (PCEPH) should be adjusted for freeway grade and truck volumes. Table 504.7C and Figures 504.7D 504.8 Access Control and E are reprinted from the 1965 HCM and provide Access rights shall be acquired along interchange information regarding vehicle distribution by lane. ramps to their junction with the nearest public The results obtained from Figure 504.7A (the Leisch road. At such junctions, for new construction, Method) for single-lane ramps with an auxiliary lane access control should extend 100 feet beyond the and weaving rates exceeding 2500 PCEPH should end of the curb return or ramp radius in urban areas be checked using the LOS D method. and 300 feet in rural areas, or as far as necessary to ensure that entry onto the facility does not impair Weaving capacity analyses other than those operational characteristics. Access control shall described above should not be used on California HIGHWAY DESIGN MANUAL 500-39 March 20, 2020 extend at least 50 feet beyond the end of the curb return, ramp radius, or taper. Typical examples of access control at interchanges are shown in Figure 504.8. These illustrations do not presume to cover all situations or to indicate the most desirable designs for all cases. When there is state-owned access control on both sides of a local road, a maintenance agreement may be needed. For new construction or major reconstruction, access rights shall be acquired on the opposite side of the local road from ramp terminals to preclude driveways or local roads within the ramp intersection. This access control would limit the volume of traffic and the number of phases at the intersection of the ramp and local facility, thereby optimizing capacity and operation of the ramp. Through a combination of access control and the use of raised median islands along the local facility, right–in/right-out access may be permitted beyond 200 feet from the ramp intersection. The length of access control on both sides of the local facility should match. See Index 504.3(3) for further ramp intersection guidance on the crossroads. In Case 2 consider private ownership within the loop only if access to the property is an adequate distance from the ramp junction to preserve operational integrity. In Case 3 if the crossroads is near the ramp junction at the local road, full access control should be acquired on the local road from the junction to the intersection with the crossroad. Case 6 represents a slip ramp design. If the ramp is perpendicular to the local/frontage road refer to Case 3. In Case 6 if the crossroad is near the ramp junction to the local/frontage road, access control should be acquired on the opposite side of the local road from the junction. 500-40 HIGHWAY DESIGN MANUAL December 16, 2016

Figure 504.7A Design Curve for Freeway and Collector Weaving HIGHWAY DESIGN MANUAL 500-41 December 16, 2016

Figure 504.7B Lane Configuration of Weaving Sections

500-42 HIGHWAY DESIGN MANUAL December 16, 2016

Table 504.7C Percent of Through Traffic Remaining in Outer Through Lane (Level of Service D Procedure)

Total Volume of Approximate Percentage of Through(1) Traffic Remaining in the Outer Through Through Traffic, Lane in the Vicinity of Ramp Terminals at Level of Service D One Direction (2) (3) (4) (vph) 8-Lane Freeway 6-Lane Freeway 4-Lane Freeway 6500 and over 10 - - 6000 - 6499 10 - - 5500 - 5999 10 - - 5000 - 5499 9 - - 4500 - 4999 9 18 - 4000 - 4499 8 14 - 3500 - 3999 8 10 - 3000 - 3499 8 6 40 2500 - 2999 8 6 35 2000 - 2499 8 6 30 1500 - 1999 8 6 25 Up to 1499 8 6 20

NOTES: (1) Traffic not involved in a ramp movement within 4,000 feet in either direction. (2) 4 lanes one-way. (3) 3 lanes one-way. (4) 2 lanes one-way. HIGHWAY DESIGN MANUAL 500-43 December 16, 2016

Figure 504.7D Percentage Distribution of On- and Off-ramp Traffic in Outer Through Lane and Auxiliary Lane (Level of Service D Procedure) 500-44 HIGHWAY DESIGN MANUAL December 16, 2016

Figure 504.7E

Percentage of Ramp Traffic in the Outer Through Lane (No Auxiliary Lane) (Level of Service D Procedure)

A - NORMAL CALCULATION B - CHECK CALCULATIONS

2 LANES ONE-WAY BECAUSE % IN THE OUTER THROUGH LANE AT 1,500’ IS BELOW DASHED LINE, RECALCULATE ASSUMING ON-RAMP TRAFFIC IS THROUGH "THROUGH TRAFFIC" = 2,400 VPH TRAFFIC. "ON-RAMP" = 800 VPH AMOUNT IN THE OUTER THROUGH LANE AT 1 AMOUNT IN THE OUTER THROUGH LANE AT 1 THROUGH (FROM TABLE 504.7C) 0.40 X 3,200 = 1,280

THROUGH (FROM TABLE 504.7C) = 0.30 X 2,400 = 720 SINCE CALCULATION B (1,280) IS GREATER THAN

ON-RAMP (FROM CHART ABOVE) = 0.30 X 800 = 240 CALCULATION A (960) USE 1,280.

960

*THESE PERCENTAGES ARE NOT NECESSARILY THE DISTRIBUTIONS UNDER FREE FLOW OR LIGHT RAMP TRAFFIC, BUT UNDER PRESSURE OF HIGH VOLUMES IN THE RIGHT LANES AT THE LOCATION BEING CONSIDERED AND WITH AVAILABLE ROOM IN OTHER LANES.

NOTE: IF RAMP PERCENTAGE IN THE OUTER THROUGH LANE AT POINT UNDER CONSIDERATION IS BELOW DASHED LINE, THEN AMOUNT IN THE OUTER THROUGH LANE SHOULD BE RECALCULATED ASSUMING RAMP TRAFFIC IS THROUGH TRAFFIC. USE HIGHER VALUE. SEE EXAMPLE ABOVE.

HIGHWAY DESIGN MANUAL 500-45 December 16, 2016

Figure 504.8 Typical Examples of Access Control at Interchanges

500-46 HIGHWAY DESIGN MANUAL December 16, 2016

Figure 504.8 (cont.) Typical Examples of Access Control at Interchanges