Objective: The objective of this project was to develop design guidance or criteria addressing the safety and operational tradeoffs for motorists, pedestrians, and bicyclists for three specific topics: selecting lane widths, channelizing right turns, and using right-turn deceleration lanes at driveways and unsignalized intersections. This project was intended to address urban and suburban arterials and collectors with speeds of 45 mph or less. For this project, consideration of pedestrians should include a full range of ages and visual, as well as other, impairments.
Status: The research is complete and three syntheses were developed.
Background: Urban and suburban transportation corridors are becoming increasingly congested. At the same time, adding width to roadways and streets often results in higher running speeds and increased pedestrian crossing distances, which in turn can act to decrease the safety and livability of the communities through which the roadways and streets pass. Further, additional space for roadways and walkways is often extremely limited or simply not available. Therefore, it is important that the roadway width be optimized in terms of safety and operational efficiency. Lane widths of 10, 11, and 12 feet are the most commonly used in these situations. Traditionally, the wider lane has been thought to maximize operational capacity. Recently, questions have been raised concerning whether narrower lanes may have similar capacity capabilities and perhaps enhanced safety characteristics compared with the wider lanes in low-speed applications.
Channelized right turns have become increasingly common in urban areas over the last 20 years, significantly reducing emissions from idling vehicles as well as enhancing intersection capacity and operations. However, there is concern that conflicts between vehicles and pedestrians increase at channelized right turns because the driver's attention is focused on the cross-street traffic.
Right-turn deceleration lanes reduce the incidence of rear-end collisions from vehicles slowing to make right-turn maneuvers. Right-turn deceleration lanes also improve arterial capacity by removing slower moving vehicles from the main traffic stream. New access points, particularly busy commercial driveways, often contribute noticeably to congestion and reduced outside travel lane capacity. Several states have established application and design criteria for right-turn deceleration lanes for driveways and intersections, but the criteria vary widely from state to state. In addition, there is little information on the design and placement of bicycle lanes and handling of adjacent pedestrian paths at locations with right-turn deceleration lanes. Information is needed for transportation agencies to use in determining when a deceleration lane is needed and in designing that lane.
Tasks: To accomplish the project objective, the following tasks are envisioned: (1) Critically analyze and synthesize current literature and state and local standards, policies, and practices on the safety and operational tradeoffs of various lane widths, primarily 9-, 10-, 11-, and 12-foot wide lanes (exclusive of curb offsets) with respect to mode (pedestrians, bicycles, and motorized vehicles). Identify research efforts needed to ascertain the safety and operational tradeoffs for the various modes. Document the results in a form suitable for publication as a contractor's draft on the NCHRP's web site. (2) Critically analyze and synthesize current literature and state and local standards, policies, and practices with respect to the design, safety, and operations of channelized right turns. The synthesis and analysis should focus on the interaction between vehicles and pedestrians. Specific attention should be given to the needs of visually impaired pedestrians in crossing from the curb to the island in channelized right-turn situations. Turn radius should be considered, both in terms of slowing turning vehicle traffic and permitting emergency-vehicle operations. Identify research efforts needed to develop practical methods of mitigating conflicts and of determining the effects of the methods on operations. Document the results in a form suitable for publication as a contractor's draft on the NCHRP's web site. (3) Critically analyze and synthesize current literature and state and local standards, policies, and practices on application criteria and design guidance for right-turn deceleration lanes at driveways and unsignalized intersections. Highlight the effects on bicycle and pedestrian conflicts. Discuss how the information could be applied at signalized intersections where the right-turn deceleration lane is justified for safety and operational reasons, as opposed to strictly capacity needs. Identify research efforts needed to develop application criteria and design guidance. Document the results in a form suitable for publication as a contractor's draft document on the NCHRP's web site. (4) Assign priorities to the research efforts identified in Tasks 1 through 3. Develop detailed data-collection and analysis plans for addressing high-priority efforts commensurate with the resources remaining and for a limited number of alternates. The plans must include schedules and budgets. (5) Submit an interim report, within 8 months, to document Tasks 1 through 4. (6) Execute the research plans as approved by the project panel at the interim meeting. (7) Refine the syntheses developed in Tasks 1 through 3 based on the results of Task 6 and any comments that have been received on the draft documents. Incorporate recommended design guidance and criteria into each to produce guidelines. (8) Submit a final report that documents the entire research effort and includes the three topical guidelines as separate chapters. Where appropriate, the report should include an appendix with recommended language for the AASHTO Policy on Geometric Design of Highways and Streets; the AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities (forthcoming); the AASHTO Guide for the Development of Bicycle Facilities; the Manual on Uniform Traffic Control Devices; and the Traffic Control Devices Handbook.