Design Guidance for Intersection Auxiliary Lanes (2014) / Chapter Skim
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Pages 7-31
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From page 7... ...
7 Review of Literature and State Design Guidance The following sections describe recent research efforts related to design elements and considerations for auxiliary lanes at intersections. Although much of the recent research investigated aspects of left-turn lanes as drivers approach intersections, there were also findings related to right-turn lanes and to acceleration lanes downstream of intersections.
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8• The New Jersey manual references the Harmelink paper directly. FHWA's Signalized Intersections: Informational Guide (7)
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9 and accident experience when considering right-turn lanes. In rural areas, focus is primarily on a combination of through and right-turning volume.
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10 Deceleration length assumes that moderate deceleration will occur in the through-traffic lane and the vehicle entering the left-turn lane will clear the through-traffic lane at a speed of 10 mph slower than through traffic. Where providing this deceleration length is impractical, it may be acceptable to allow turning vehicles to decelerate more than 10 mph before clearing the through-traffic lane.
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11 that the value of 25 ft per vehicle used by the CORSIM modeling software was a severe underestimation for determining queue lengths, as was the 3-ft distance between vehicles. He developed new models for estimating average queue lengths and maximum lengths at a given probability; those models were based on an intervehicle spacing of 12 ft, a passenger car length of 15 ft, a 65-ft length for combination trucks, and 30 ft for other vehicles.
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12 regression equations for the turning movements at an unsignalized intersection. Gard compared these equations to the procedures found in the 2000 Highway Capacity Manual, the monograph in the Institute of Transportation Engineers' (ITE's)
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13 • Opposing Traffic for the PPLT Signal Scheme: The volume of the opposing flow has no significant effect on the leftturn lane length as long as the approach left-turn volume is small. When the derived lane length becomes substantially longer than what AASHTO recommends and the space for it is not available, the framework allows the basis to consider changing the signal scheme such that the increase of the length can be kept to a minimum.
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14 by Jack E Leisch and Associates (25)
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15 Left-Turn Volume (veh/hr) Storage Length, Rounded Up to Nearest 25-ft Increment (ft)
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16 of the full width of the turn lane. This condition is known as a fully shadowed left-turn lane.
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17 the likelihood that entry into the left-turn lane may spill back into the through lane. Municipalities and urban counties are increasingly adopting the use of taper lengths such as 100 ft for a single-turn lane and 150 ft for a double-turn lane for urban streets (4)
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18 used to reinforce the action the driver is expected to take. It is important that appropriate vehicle storage length be provided because, with no median protection, the excess queue will extend into the through travel lane.
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19 value used in the HCM. Because data were limited to queue lengths between 8 and 11 vehicles, the research results did not directly address queue lengths longer than 11 vehicles.
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20 performance of different designs to enable engineers in setting policy, establishing project-level design, and discussing the impacts of medians with business and property owners. As documented in NCHRP Report 524 (35)
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21 the safety experience of different right-turn lane designs. Their evaluations found that the variables affecting the turning speed at an exclusive right-turn lane included the type of channelization present (either lane line or raised island)
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22 type of offset geometry may also be used for trucks turning right with long rear overhangs (4)
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23 study because it could use multiple study sites across the nation to collect a large amount of data for a robust statistical analysis. • There are no geometric guidelines for designers to use when deciding key elements of three-dimensional features of the offset right-turn lane that can generate poor choices by through, right-turning, and left-turning drivers on major roads and stopped drivers at minor road approaches of two-way stop-controlled intersections exhibiting ORTLs.
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24 • Orientation and mobility specialists have a strong preference for raised islands with cut-through pedestrian paths because they provide better guidance and information about the location of the island for pedestrians with vision impairment than painted islands. • When right-turn volumes are high and pedestrian and bicycle volumes are relatively low, capacity considerations may dictate the use of larger radii, which enable higherspeed, higher-volume turns.
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25 roadways much more difficult. The Highway Safety Manual (1)
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26 Worth and Houston urban areas. They reported the following as key findings for TLT lanes: • Lane utilization patterns were varied for each of the five sites studied.
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27 guide through traffic around the left-turn lane. The typical length of the approach taper for a bypass lane is the same as that used for a shadowed or partially shadowed lane when through traffic is shifted to the right.
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28 results in the simultaneous movement of left-turning traffic with through traffic at the intersection. The key trade offs are the need for additional right-of-way to accommodate the displaced lanes and the creation of several smaller ancillary intersections around the primary intersection, which must also be maintained with signing and marking.
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29 that drivers neither accelerate at constant rates, nor at rates as high as those identified in the AASHTO Green Book. In addition, drivers in free-flow conditions do not typically use the entire length of the speed-change lane when it is provided.
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30 capacity. However, the conditions for their effective use and their effect on safety, operation, and the environment have yet to be documented.
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31 Qu eu e S tor ag e Le ng th En te rin g Ta pe r Le ng th D ec el er at io n Le ng th Tu rn -L an e W id th Ch an ne liz at io n/ Is la nd D es ig n O ffs et L ef t-t ur n La ne s D ou bl e (or D ua l)
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