RESEARCH PROBLEM STATEMENT
The American Association of State Highway and Transportation Officials’ (AASHTO) Roadside Design Guide (RDG) contains median barrier type, selection, and placement guidelines for implementation on divided highways. The formulation of these guidelines has resulted from retrospective studies of median-related crashes and the results of crash testing barriers under idealized installation conditions. Crash-based studies have shown that installation of median barriers reduces the frequency of severe, cross-median collisions; however, the trade-off is an increase in median barrier collisions.
Approximately 20 percent of motor vehicle fatalities are classified as single-vehicle, run-off-the-road (SVROR), hit fixed object collisions. Traffic barriers are the fixed objective struck in 8 percent of fatal SVROR crashes. Use of median barrier has increased on divided highways in the U.S. in an effort to prevent cross-median crashes. A variety of barrier systems, such as low- and high-tension cable, w-beam, and concrete barrier systems are used, depending on site conditions.
NCHRP Report 490 In Service Performance of Traffic Barriers developed procedures that transportation agencies can use as a framework for performing in-service performance evaluations of roadside safety features. A pilot study was used to demonstrate the procedures. The research concluded that in-service performance evaluations should be integrated more fully into the design, testing, and evaluation of roadside hardware. The purpose of this research project is to conduct a large-scale in-service performance evaluation of median barrier applications on divided highways using the procedures developed in NCHRP Report 490. These data should then be analyzed and used to develop a performance-based framework for selecting median barriers based on expected impact performance, installation and maintenance costs, and placement location conditions (e.g., soil, median slope, etc.).
LITERATURE SEARCH SUMMARY
Research efforts that are either recently completed or are currently underway that relate to the problem statement include:
q NCHRP Report 490, In Service Performance of Traffic Barriers, which developed general procedures for in-service performance evaluations.
q NCHRP Project 22-21, Median Cross-section Design for Rural Divided Highways, which intends to develop median cross-section design guidelines for rural divided highways using both crash-based and vehicle dynamics simulations studies.
q NCHRP 22-22 Placement of Traffic Barriers on Roadside Slopes, which is to produce comprehensive recommendations for placement of barriers on roadside and median slopes using a combination of simulations and crash testing procedures.
q Performance Evaluation of Cable Median Barrier Systems in Texas. Report No. FHWA/TX-09/0-5609-1, Texas Transportation Institute, College Station, TX, August 2009.
The principal research objectives include:
1. Conduct a large-scale in-service performance evaluation of median barrier applications on divided highways.
2. Develop an electronic database with all in-service performance data that can be upgraded by transportation agencies as additional data are collected over time.
3. Employ appropriate statistical procedures to analyze the data collected.
4. Using the statistical analysis results, develop a framework that can be integrated into the AASHTO RDG which enables state transportation agencies to select median barrier types based on expected impact performance, installation and maintenance costs, and median site characteristics.
It is anticipated that this research would be conducted in two phases. The first phase would include the following tasks:
a. Perform a criteria review of the published literature related to the in-service performance evaluation of traffic barriers.
b. Based on the results of the review, formulate a data collection plan that will enable an adequate sample of in-service performance data to be collected for subsequent analysis in Phase II of the research. The data collection plan should consider geographic coverage and median barrier types.
c. Develop a plan to analyze the data collected.
d. Prepare an outline of the proposed framework that will be developed after concluding the statistical analysis of in-service data.
e. Submit a Phase I interim report and meet with the panel to review the findings of the report.
Pending approval of the first project phase, a second phase should be undertaken to execute the Phase I plan. This phase will include the data collection, analysis, and framework for integrating the results into Chapter 6 of the AASHTO RDG.
ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD
Recommended Funding: $750,000.
Research Period: 36 months.
URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION
The implications of this research are broad-based and will directly assist designers in selecting median barriers for installation on existing or planned divided highways. Urgency is high and the potential payoff of this research is substantial. The implementation would be via the AASHTO RDG other state and local roadside design guidelines. The project would also create an electronic database that could be upgraded in the future as additional in-service performance evaluation data become available. Such a data resource would enable researchers to continually assess and improve median barrier type and selection guidelines based on performance. The TRB Committees on Geometric Design and Operational Effects of Geometrics jointly sponsor this research needs statement. The AASHTO Technical Committee on Geometric Design collaborated on the research idea at a joint work session with the TRB committees in 2011.