Intersection Design To Accommodate Pedestrian Crosswalk Cross Slope
Research Problem Statement
The Americans with Disabilities Act (ADA) requires that public rights-of way, including sidewalks and crosswalks, be accessible to pedestrians with disabilities. The U.S. Access Board's ADA accessibility guidelines specify the minimum level of accessibility in new construction and alteration projects and serves as the basis for standards enforced and maintained by other agencies. ADA guidelines require that the cross slope in crosswalks should not exceed 2% measured perpendicular to the direction of pedestrian travel. Many transportation agencies are looking for guidance on working with these proposed provisions.
Many of the potential treatments used to achieve the required cross slope on crosswalks do not conform to existing highway design and construction standards. In addition, tabling the crosswalk or intersection would require adjustments in the vertical alignment of the roadway which would impact street drainage. Tabling crosswalks or intersections may also have unintended negative impacts on the control and safety of motor vehicles and their occupants. These concerns are heightened for emergency vehicles. Loss of control of vehicles in urban areas could have tremendous safety implications for pedestrians alongside the roadway.
Literature Search Summary
A search of TRIS online and the Research in Progress databases did not identify any research specifically addressing the interaction between roadway design and pedestrian crosswalk cross slopes.
Better information is needed about the introduction of reduced street grades at pedestrian crosswalks for roadways on steep longitudinal grades. Since the cross slope of the crosswalk is also the longitudinal grade of the street being crossed, this requirement impacts the vertical alignment of the roadway in the vicinity of the intersection. The impact that tabled intersections would have on motorist safety and street drainage needs to be examined along with potential platform designs to safely accommodate vehicles on streets with steep grades, while meeting the crosswalk cross slope requirements.
Accomplishment of the project objective will include at least the following tasks:
Task 1. Review the existing geometric design, hydraulic design, and other relevant literature (both domestic and international) to (a) Document the current state of practice with respect to tabled intersection design, drainage, vehicle dynamics, and the safety of users of all modes, (b) document the safety of various designs on the various modes, and (c) determine engineering policies and practices that may need to be revised as a result of the anticipated recommendations from this research effort.
Task 2. Select an appropriate number of sites with and without tabled intersections and conduct field studies. Sites should be those utilized by as many different modes as possible and the interactions between the modes should be documented.
Task 3. Analyze accident/crash reports for the above sites and document the number and type of accidents and the modes involved at each location.
Task 4. Simulate the impact on various modes for different designs of tabled intersections and develop recommendations for design policy.
Task 5. Submit a final report that documents the entire research effort, recommends design criteria for intersection design on various classes of roadways and in various types of terrain, and includes the products of Tasks 1 through 4. Where appropriate, the report should include appendices 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; and other documents as appropriate.
Estimate of Problem Funding and Research Period
Urgency, Payoff Potential, and Implementation
State and local transportation agencies would use the information obtained from the research project to develop guidelines for the intersection design for various facilities and with varying terrain conditions. This would result in a transportation system that better considers all modes and provides the safest design for all users, based on site-specific conditions. Documents that would potentially be affected are the AASHTO Policy on Geometric Design of Highways and Streets; and the AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities.