Guidelines for Cost-Effective Safety Treatments of Roadside Ditches

Roadside ditches or swales are integral features of highways and are critical for control of stormwater runoff. These features can be obstacles to errant motorists that leave the roadway. The Fatality Analysis Reporting System (FARS) indicates that over the past 15 years more than 1,000 fatalities annually are attributed to ditches. The AASHTO Roadside Design Guide provides some guidance on preferred configurations for ditches. However, this guidance is based on the results of limited testing and simulations conducted in the 1970s. Additionally, there is variation in the practices across the states for designing and maintaining ditches—and for many miles of roads, the ditches are a remnant of much older design standards. Limited right-of-way often dictates the configuration of ditches and in many cases the preferred configurations are not practical. Enclosed drainage systems are expensive and may result in additional requirements for treatment and discharge of the runoff. Other drainage elements such as culvert ends, inlets, headwalls, and holding basins may themselves become roadside obstacles. Installing a barrier to shield a ditch reduces the available clear zone, is not cost-effective in many cases, and presents maintenance and operational issues. The need exists to reduce the number and severity of crashes involving roadside ditches. By identifying factors involved in crash events and evaluating the dynamics of vehicles interacting with ditch elements, countermeasures can be developed and implemented to mitigate these crashes. The objective of this research is to develop guidelines for cost-effective treatments of roadside ditches and appurtenances in order to reduce the severity of ditch crashes. Tasks include: (1). Conduct a literature review of domestic and international literature that address the safety performance of roadside slopes and ditch designs. (2). Conduct a survey of state departments of transportation (DOTs) and Canadian provincial transportation agencies to identify innovative treatments that may not have been previously documented. The NCHRP will approve the survey prior to its dissemination. (3). Analyze existing roadway and crash data to identify any trends in the type and severity of ditch-related crashes and their relationship to ditch geometry, roadway characteristics, vehicle type, presence of appurtenances, and other relevant characteristics. Potential data sources include state databases; Fatal Analysis Reporting System (FARS); NCHRP Report 665, Identification of Vehicular Impact Conditions Associated with Serious Ran-off-Road Crashes;" and National Automotive Sampling System (NASS). (4). Identify ditch configurations associated with high-severity crashes and propose potential strategies for reducing the number and severity of those crashes. Indicate the degree to which individual strategies will impact hydraulic capacity. (5). Submit an interim report summarizing the findings of Tasks 1 through 4 including a revised work plan that outlines how the effectiveness of each strategy will be evaluated in Task 7. The evaluation may include, but is not limited to, simulation, full-scale crash testing, and cost-effectiveness analysis. (6). Approximately 1 month after submittal of the interim report, meet with the NCHRP panel to review the report and proposed work plan. Work on Task 7 will not begin without prior approval of the NCHRP. (7). Execute the approved work plan to evaluate the effectiveness of potential strategies. (8). Draft guidelines for the design and treatment of roadside ditches that consider, at a minimum, risk factors, cost effectiveness, feasibility, road geometry, and traffic. Guidelines should be written in a format suitable for potential inclusion in the AASHTO Roadside Design Guide. (9). Submit a final report documenting the entire research effort. Include the proposed guidelines in a stand-alone appendix, in a format suitable for consideration by AASHTO.


  • English


  • Status: Active
  • Contract Numbers:

    Project 16-05

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Bush, Mark

  • Performing Organizations:

    Texas A&M Research Foundation, College Station

    Texas A&M University
    College Station, TX  United States  77843
  • Principal Investigators:

    Bullard, D

  • Start Date: 20100514
  • Expected Completion Date: 20180731
  • Actual Completion Date: 0
  • Source Data: RiP Project 22364

Subject/Index Terms

Filing Info

  • Accession Number: 01464189
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 16-05
  • Files: TRB, RiP
  • Created Date: Jan 3 2013 2:37PM