Design Guidance for Channelized Right-Turn Lanes (2014)

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Appendix B Revised Text on Channelized Right-Turn Lanes for the AASHTO Green Book This appendix presents revised text on channelized right-turn lanes for consideration by AASHTO for potential inclusion in a future edition of the AASHTO Policy on Geometric Design of Highways and Streets (1), commonly known as the Green Book. The first page of text should replace the discussion in Chapter 9 in the section entitled “Types and Examples of Intersections,” subsection “General Considerations,” that appears on Page 558 of the 2004 Green Book. On this first page of text, modified text is shown in a bold font. It is not intended that this bold font should be used in the Green Book. The subsequent pages of text should be inserted in Chapter 9 as a new subsection under “Types of Turning Roadways,” which begins on Page 583 of the 2004 Green Book. The recommended title of this new subsection is “Channelized Right-Turn Lanes.” The new subsection could potentially be inserted before the subsection on “Minimum Edge-of-Traveled- Way Designs.” This text is entirely new, so no bold font is used to identify changes. The research team recommends that the term “free-flow right turns” be replaced with the term “channelized right-turn lanes” throughout Chapter 9 of the Green Book. The Green Book is currently in the publication process for a major update. If this update is complete, this page in the revised final report for Project 3-89 will be updated accordingly.

Types and Examples of Intersections General Considerations The basic types of intersections are the three-leg or T, the four-leg, and the multileg. At each particular location, the intersection type is determined primarily by the number of intersecting legs, the topography, the character of the intersecting highways, the traffic volumes, patterns, and speeds, and the desired type of operation. Any of the basic intersection types can vary greatly in scope, shape, and degree of channelization. Once the intersection type is established, the design controls and criteria discussed in Chapter 2 and the elements of intersection design presented in Chapter 3, as well as in this chapter, should be applied to arrive at a suitable geometric plan. In this section each type of intersection is discussed separately, and likely variations of each are shown. It is not practical to show all possible variations, but those presented are sufficient to illustrate the general application of intersection design. Many other variations of types and treatment may be found in the NCHRP Report 279, Intersection Channelization Design Guide (2), which shows detailed examples that are not included in this policy. Although many of the intersection design examples are located in urban areas, the principles involved apply equally to design in rural areas. Some minor design variations occur with different kinds of traffic control, but all of the intersection types shown lend themselves to cautionary or non-stop control, stop control for minor approaches, four-way stop control, and both fixed-time and traffic-actuated signal control. Right turns without stop or yield control are sometimes provided at channelized intersections. Such channelized right-turn lanes should be used only where an adequate merge is provided. Where motor vehicle conflicts with pedestrians or bicyclists are anticipated, provisions for pedestrians and bicycle movements must be considered in the design. Channelized right-turn lanes have a definite role in improving operations and safety at intersections. However, at locations with high pedestrian volumes, the use of channelized right-turn lanes should be considered only where significant traffic capacity or safety problems may occur without them and adequate pedestrian crossings can be provided. Simple intersections are presented first, followed by more complex types, some of which are special adaptations. In addition, conditions for which each intersection type may be suited are discussed below. B-1

Channelized Right-Turn Lanes 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. Crosswalk Location A pedestrian crosswalk could potentially be placed at any location along a channelized right- turn roadway (e.g., upstream, center, or downstream). It is obviously desirable to place the crosswalk at whatever location would maximize safety, presumably the location where pedestrians who are crossing or about to cross the right-turn roadway are most visible to motorists and where motorists are most likely to yield to pedestrians. A majority of the sites (nearly 70 percent) evaluated by Potts et al. (2) 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. Consistency of crosswalk location at channelized right-turn lanes is important to pedestrians with vision impairment, and current highway agency practice indicates a 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 at the entry to the cross street, the crosswalk should be located beyond the stop line at that point. 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 entry to the cross street at the downstream end of 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. B-2

Special Crosswalk Signing and Marking Marked crosswalks are the primary means of indicating the presence of a pedestrian crossing. However, drivers do not always yield the right-of-way to pedestrians simply because they are in a crosswalk. Other special crosswalk signing and marking treatments have been considered for use at pedestrian crossings on channelized right-turn roadways to enhance crossing safety for pedestrians, in general, and for pedestrians with vision impairment. These include: • Use of a 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) • 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) Additional signing and pedestrian crosswalk treatments may improve the motorist yield behavior and pedestrian use of the crosswalk. Island Type A channelized right-turn lane consists of a right-turning roadway at an intersection, separated from the through travel lanes of both adjoining legs of the intersection by a channelizing island. At right-angle intersections, such channelizing islands are roughly triangular in shape, although the sides of the island may be curved, where appropriate, to match the alignment of the adjacent roadways. Islands serve three primary functions: (a) channelization— to control and direct traffic movement, usually turning; (b) division—to divide opposing or same direction traffic streams; and (c) refuge—to provide refuge for pedestrians. Most islands combine two or all of these functions. Islands for channelized right-turn lanes typically serve all three functions. The edges of channelizing islands may be defined by raised curbs or may consist of painted pavement or turf that is flush with the pavement. Most channelizing islands in urban areas are defined by raised curbs. Curbed islands are considered most favorable for pedestrians because curbs most clearly define the boundary between the traveled way, intended for vehicle use, and the island, intended for pedestrian refuge. Curbed islands can improve the safety for pedestrians by allowing them to cross the street in two stages. Raised islands with “cut-through” pedestrian paths are important to pedestrians with vision impairment because they provide better guidance and information about the location of the island than painted islands. Where curb ramps are provided, truncated dome detectable warnings are required at the base of the ramp, where it joins the street, to indicate the location of the edge of the street to pedestrians with vision impairment. B-3

Radius of Turning Roadway Design criteria for the radii of channelized right-turn roadways are a function of turning speeds, truck considerations, pedestrian crossing distances, and resulting island sizes. Channelized right-turn lanes provide one method for accommodating larger turning radii without widening the major-street pedestrian crossings and without increasing the intersection pavement area. Where right-turn volumes are high and pedestrian and bicycle volumes are relatively low, capacity considerations may dictate the use of larger radii, which enable higher-speed, higher- volume turns. However, small turning radii, which promote low-speed right turns, are appropriate where such turns regularly conflict with pedestrians, as higher speeds have been shown to result in a decrease in yielding to pedestrians by motorists. 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: • A flat-angle entry to the cross street • A nearly-right-angle entry to the cross street The two designs 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. Deceleration Lanes Drivers making a right-turn maneuver at an intersection are usually required to reduce speed before turning. Significant deceleration that takes place directly on the through traveled way may disrupt the flow of through traffic and increase the potential for conflicts with through vehicles. To minimize deceleration in the through travel lanes, deceleration lanes should be considered. Right-turn deceleration lanes provide one or more of the following functions (4): • A means of safe deceleration outside the high-speed through lanes for right-turning traffic. • A storage area for right-turning vehicles to assist in optimization of traffic signal phasing. B-4

• A means of separating right-turning vehicles from other traffic at stop-controlled intersection approaches. The addition of a deceleration lane at the approach to a channelized right-turn lane provides an opportunity for motorists to safely slow down prior to reaching the crosswalk area at the turning roadway. Acceleration Lanes Acceleration lanes provide an opportunity for vehicles to complete the right-turn maneuver unimpeded and then accelerate parallel to the cross-street traffic prior to merging. Channelized right-turn lanes with acceleration lanes 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. Pedestrian Signals Pedestrian signals can be used at pedestrian crossings on channelized right-turn roadways to enhance crossing safety for pedestrians, particularly for pedestrians with vision impairment. Where a signal is provided for pedestrians to cross a channelized right-turn lane, a pedestrian- actuated signal should be considered. B-5

References 1. American Association of State Highway and Transportation Officials, A Policy on Geometric Design of Highways and Streets, 2004. 2. Potts, I. B., D. W. Harwood, K. M. Bauer, D. K. Gilmore, J. M. Hutton, D. J. Torbic, J. F. Ringert, A. Daleiden, and J. M. Barlow, NCHRP Web-Only Document 208: Design Guidance for Channelized Right-Turn Lanes, Transportation Research Board of the National Academies, Washington, D.C., 2011. 3. Potts, I. B., D. W. Harwood, D. J. Torbic, D. K. S. A. Hennum, C. B. Tiesler, J. D. Zegeer, J. F. Ringert, D. L. Harkey, and J. M. Barlow, Synthesis on Channelized Right Turns on Urban and Suburban Arterials, Final Report, NCHRP Project 3-72, Midwest Research Institute, August 2006. 4. Neuman, T. R., NCHRP Report 279: Intersection Channelization Design Guide, NCHRP Report 279, TRB, National Research Council, Washington, D.C., 1985. B-6