NCHRP 17-21 [Completed]
Safety of U-Turns at Unsignalized Median Openings
| Project Data
||Midwest Research Institute|
||Ingrid Anderson Potts|
Background: Many state and local transportation agencies are considering installing nontraversable medians on multilane highways. Business and property owners often resist these improvements. One of the arguments made is that the number of U-turning vehicles will increase. However, the impact of an increase in U-turns on the safety of the road is not clear. Studies attributing safety gains to a nontraversable median have not focused on the specific situation at the median opening, either isolated or at an intersection, where U-turns occur.
After a nontraversable median has been installed, agencies are often approached by abutting property owners who desire a new median opening. Additional information would be helpful in reviewing these requests, determining if an opening should be allowed, and developing a design that does not unduly impact the safety or operation of the road.
There is a wide variety of designs for nontraversable medians. A thorough review of the safety and operational impacts of the various designs would be beneficial, both in setting design policy and in project-level design.
Objective: The objectives of this research are to document the safety impacts of U-turns at unsignalized median openings and to develop a guide for the use, location, and design of unsignalized median openings for U-turns.
Tasks: Accomplishment of the project objectives will require the following tasks: (1) Analyze, describe, and critique pertinent literature on the safety and operation of U-turns at unsignalized median openings. (2) Survey state and local transportation agencies to determine current design practices and policies related to unsignalized median openings for U-turns. Conduct selective interviews to gain further insight into experiences with various designs. (3) Identify typical median-opening designs, and hypothesize the potential safety impacts and operational effects associated with each design for various road, roadside, and traffic conditions. (4) Submit an interim report, within 9 months, documenting Tasks 1 through 3. The interim report shall contain a detailed work plan for quantifying the safety impacts of various unsignalized median-opening designs in Task 5. The interim report shall also include an outline of the project final report. (5) As far as project resources allow, quantify the safety impacts of the most promising designs identified in Task 3 in accordance with the approved Task 4 work plan. (6) Submit a clear and concise final report that documents the entire research effort and includes a section dedicated to practical application of the knowledge obtained. This section should use a handbook format and recommend median-opening designs, identify the circumstances where they are appropriate, and estimate the likely impact on safety and operations. Preliminary design drawings should be submitted as electronic files using a common computer-aided drafting format. Any recommendations for improvements to the AASHTO Policy on Geometric Design of Highways and Streets should be included as an appendix to the report.
Product Availability: The final report was published as NCHRP Report 524.