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Chapter 6. Interpretation of Results and Design Guidance This chapter presents the interpretation of the research results and provides a basis for the design guidance presented in the guidelines in Appendix A. This guidance compares approaches with channelized right-turn lanes (CRT), shared through/right-turn lanes (SRT), and conventional right-turn lanes (RTL). These configurations are illustrated in Figure 36. Figure 36. Illustration of Three Right-Turn Treatment TypesâSTR, RTL, and CRT. 93
Application of Channelized Right-Turn Lanes 6.1 The research results indicate that channelized right-turn lanes have a definite role in improving operations and safety at intersections. However, to achieve these benefits they should have consistent design and traffic control and should be used at appropriate locations. Results of the observational field studies in Chapter 3 of this report suggest that, overall, pedestrians do not have difficulty crossing channelized right-turn lanes. Most pedestrians cross in the crosswalk and obey pedestrian signals. Most motorists yield to pedestrians once they are in the crosswalk of a channelized right-turn lane, either by stopping or reducing their speed. Fewer motorists in channelized right-turn lanes yield to pedestrians waiting at the curb to cross, although such failure to yield is typical of most pedestrian crossings and is not unique to channelized right-turn lanes. When stopped in a queue, motorists keep the crosswalk open to pedestrians. Avoidance maneuvers, either by a pedestrian or a motorist, were observed in less than 1 percent of the pedestrian crossings. The traffic operational analysis in Chapter 4 of this report found that channelized right-turn lanes with yield control reduce right-turn delay to vehicles by 25 to 75 percent in comparison to intersection approaches with conventional right-turn lanes. This advantage in delay reduction was observed over the full range of vehicle and pedestrian volumes considered. Vehicle delay increased proportionally faster with increasing pedestrian crossing volume for channelized right- turn lanes than for conventional right-turn lanes, but the vehicle delay for channelized right-turn lanes was always lower than for conventional right-turn lanes. Where a signal is provided for pedestrians to cross a channelized right-turn lane on a cycle coordinated with the primary signal at the intersection, vehicle delay with the channelized right- turn lane is, generally, greater than the vehicle delay for both conventional right-turn lanes and yield-controlled channelized right-turn lanes. For the configuration with a coordinated signal, the vehicle delay is independent of the pedestrian volume because the signal phase for crossing the channelized right-turn lane is called every cycle when the primary signal changes. This effect can be reduced in instances where pedestrian crossing times are dictating signal timing by providing a pedestrian-actuated signal for crossing the channelized right-turn lane; with an actuated signal, vehicle delay would be expected to increase proportionally with pedestrian crossing volume. Chapter 5 of this report presents an analysis of total crashes, rear-end crashes, sideswipe crashes, and merging crashes, for three right-turn treatment typesâchannelized right-turn lanes, conventional right-turn lanes, and shared through/right-turn lanes. No difference in the frequency of motor-vehicle crashes was found between channelized right-turn lanes and the other right-turn treatments. Pedestrian crash frequencies for CRT and STR approaches were very similar; pedestrian crash frequencies for RTL approaches were approximately 70 to 80 percent higher than CRT and RTL approaches, for average levels of pedestrian crossing volume. Thus, the results indicate that CRT and STR approaches have similar pedestrian safety performance, while RTL approaches have substantially more pedestrian crashes than either CRT or STR approaches. This is likely 94
because RTL approaches have longer pedestrian crossing distances on the through roadway than CRT or STR approaches with similar overall cross sections, because pedestrians on an RTL approach must cross not only the through lanes but also the right-turn lane. A further advantage of CRT approaches is that they have a refuge island for pedestrians, providing the opportunity for crossing the intersection in a two-step process. In addition, those pedestrians that cross two legs of an intersection with a channelized right-turn lane can complete their crossing without the need to cross the channelized right-turn lane. This eliminates a conflict with right-turning traffic that would occur for the other intersection types. The finding that CRT approaches have similar pedestrian crash frequencies to STR approaches and substantially lower pedestrian crash frequencies than RTL approaches must be considered in light of current highway agency practices for using channelized right-turn lanes. Most highway agencies choose to provide channelized right-turn lanes for locations with lower pedestrian volumes than intersections in general. For example, at the Toronto intersections evaluated in Chapter 5, the average pedestrian crossing volume was 510 pedestrians per day for CRT approaches; 1,120 pedestrians per day for RTL approaches; and 2,077 pedestrians per day for STR approaches. While the findings reported above were normalized for pedestrian volume, the general highway agency practice of using channelized right-turn lanes at intersections with lower pedestrian volumes suggests that this is a reasonable approach, and that caution should be exercised in using channelized right-turn lanes where pedestrian crossing volumes are high. For example, most channelized right-turn lanes in the Toronto database had pedestrian crossing volumes under 1,000 pedestrians per day. Design Issues Related to Channelized Right-Turn Lanes 6.2 Crosswalk Location A majority of the sites (nearly 70 percent) evaluated in the observational studies, presented in Chapter 3 of this report, had marked crosswalks located near the center of the channelized right-turn lane; only about 30 percent of crosswalks were located at the upstream or downstream end of the channelized right-turn lane. The highway agency survey conducted in NCHRP Project 3-72 (3) found that highway agencies prefer a crosswalk location near the center of a channelized right-turn lane; over 70 percent of highway agencies reported in the survey that their practice was to place crosswalks near the center of channelized right-turn lanes. There has been little research that evaluates how the crosswalk location affects crossings by pedestrians with vision impairment in terms of their ability to identify the appropriate time to cross or efficiently locate the crosswalk. While research would be desirable to provide more concrete recommendations, orientation and mobility (O&M) specialists, who teach pedestrians with vision impairment how to better traverse intersections, recommend that consistency of crosswalk location is important to pedestrians with vision impairment. Such consistency would make it easier for O&M specialists to describe a typical channelized right-turn lane to pedestrians with vision impairment and teach procedures for crossing it. 95
There is no strong technical basis for recommending one crosswalk location over another, other than the need for consistency. However, consistency in locating crosswalks is important, especially to pedestrians with vision impairment, and current practice shows a clear preference for crosswalk locations near the center of a channelized right-turn lane. And, a crosswalk location at the center of the channelized right-turn lane moves vehicle-pedestrian conflicts away from both the diverge maneuver at the upstream end of the channelized right-turn lane and, especially, from the merge maneuver at the downstream end of the channelized right-turn lane. The only potential exception to a center crosswalk location for channelized right-turn lanes is that, where STOP sign or traffic signal control is provided on the channelized right-turn lane, the crosswalk should be located beyond the stop line. In addition, at locations where the channelized right-turn lane intersects the cross street at nearly a right angle, the stop line and crosswalk may be better placed at the downstream end of the channelized right-turn lane, depending on the island size and location of sidewalk approaches. To summarize the recommended guidance for the placement of crosswalks at channelized right-turn lanes: ⢠Where the entry to the cross street at the downstream end of the channelized right-turn lane has yield control or no control, place the crosswalk near the center of the channelized right-turn lane. ⢠Where the channelized right-turn lane has STOP sign control or traffic signal control, place the crosswalk immediately downstream of the stop bar, where possible. Where the channelized right-turn roadway intersects with the cross street at nearly a right angle, the stop bar and crosswalk can be placed at the downstream end of the channelized right- turn roadway. Special Crosswalk Signing and Marking Seven of the observational field study sites (see Chapter 3 of this report) included special crosswalk signing and marking treatments. An informal comparison of pedestrian and motorist behavior was made between the sites with special crosswalk signing and marking and the other observational field study sites. The comparison suggested that the additional signage and pedestrian crosswalk treatments may improve the motorist yield behavior and pedestrian use of the crosswalk. For example, the yield behavior of motorists yielding to pedestrians waiting at the curb was slightly better (47 percent vs. 40 percent) at sites with special crosswalk treatments. This suggests that additional emphasis on signing or other treatments may be needed to increase yielding for pedestrians waiting at the curb. Enhanced features of crosswalk signing and marking that are desirable include: ⢠Use of a raised crosswalk to improve visibility of crosswalk for motorists and to better define crosswalk boundaries for pedestrians (raised crosswalks are particularly helpful to pedestrians with vision impairment). ⢠Addition of fluorescent yellow-green signs both at the crosswalk and in advance of the crossing location (to supplement the high-visibility markings). 96
⢠Use of a real-time warning device to indicate to the motorist when a pedestrian is present in the area (may be activated via passive detection technologies such as microwave or infrared or via traditional methods such as push buttons). ⢠Use of dynamic message signs (for real-time or static warning messages to motorists). Island Type The channelizing island that defines a channelized right-turn lane, particularly when bounded by raised curbs, serves as a refuge area for pedestrians, and improves safety and accessibility by allowing pedestrians to cross the street in two stages. O&M specialists have a strong preference for raised islands with âcut-throughâ pedestrian paths, which provide better guidance and information about the location of the island for pedestrians with vision impairment than painted islands. Radius of Turning Roadway The traffic operational analysis in Chapter 4 of this report found that increasing the radius of a channelized right-turn roadway reduces right-turn delay by approximately 10 to 20 percent for each 8-km/h (5-mi/h) increase in turning speed. Larger delay reductions generally occur when conflicting traffic volumes on the cross street are lower. However, vehicle delay should not be the only consideration when selecting an appropriate radius. Larger radii generally encourage higher turning speeds, and previous research (15) has shown that higher speeds can result in a decrease in yielding to pedestrians by motorists. Thus, smaller radii may be more appropriate at locations where pedestrians are anticipated. Angle of Intersection with Cross Street The alignment of a channelized right-turn lane and the angle between the channelized right- turn roadway and the cross street can be designed in two different ways (as illustrated in Figure 9 in Chapter 2): ⢠A flat-angle entry to the cross street ⢠A nearly-right-angle entry to the cross street The two designs shown in Figure 9 differ in the shape of the island that creates the channelized right-turn lane. The flat-angle entry design has an island that is typically shaped like an equilateral triangle (often with one curved side), while the nearly-right-angle design is typically shaped like an isosceles triangle. The flat-angle entry design is appropriate for use in channelized right-turn lanes with either yield control or no control for vehicles at the entry to the cross street. The nearly-right-angle entry design can be used with STOP sign control or traffic signal control for vehicles at the entry to the cross street; yield control can also be used with this design where the angle of entry and sight distance along the cross street are appropriate. 97
Acceleration Lanes Acceleration lanes at the downstream end of a channelized right-turn lane provide an opportunity for vehicles to complete the right-turn maneuver unimpeded and then accelerate parallel to the cross-street traffic prior to merging. The traffic operational analysis in Chapter 4 of this report found that the addition of an acceleration lane can reduce the right-turn delay by 65 to 85 percent, depending on the conflicting through traffic volume, and may be considered where right-turn delay is a particular problem. Acceleration lanes are only desirable where there are no driveways or other access points on the cross street within or close to the acceleration lane. In addition, channelized right-turn lanes with acceleration lanes at their downstream end appear to be very difficult for pedestrians with vision impairment to cross. Therefore, the use of acceleration lanes at the downstream end of a channelized right-turn lane should generally be reserved for locations where no pedestrians or very few pedestrians are present. Typically, these would be locations without sidewalks or pedestrian crossings; at such locations, the reduction in vehicle delay resulting from addition of an acceleration lane becomes very desirable. Traffic Control Channelized right-turn lanes with signals tied to the signal cycle of the primary intersection consistently experience more delay to right-turning vehicles than yield-controlled channelized right-turn lanes. If signalization of the right-turn movement is used, a conventional right-turn lane configuration (including right-turn on red) generally performs better than signalization of the channelized right-turn lane. However, at signalized channelized right-turn lanes, it is common for traffic engineers to provide extra green time to the right-turn movement without increasing cycle length by overlapping the right turn with the cross street left turn. Figure 37 illustrates the concept of a right-turn overlap. A potential drawback of the right-turn overlap phasing is that U-turns cannot be permitted from the cross-street left-turn lane, as they may conflict with right-turning vehicles. Thus, use of an overlap phase, or other method of providing additional green time to right-turning vehicles, can substantially reduce the delay for a signalized channelized right-turn lane, but may result in other impacts to intersection operations, such as the need to restrict U-turn maneuvers. Where a signal is provided for pedestrians to cross a channelized right-turn lane, a pedestrian-actuated signal should be considered. This can reduce vehicle delay because the phase for crossing the channelized right-turn lane is called only when pedestrians are present. 98
Figure 37. Right-Turn Overlap 99
