State departments of transportation (DOTs) continuously strive to reduce the frequency and severity of roadway departure crashes while balancing community and environmental needs, accommodation of utilities, and limited transportation budgets. The possible influence of curb on traffic safety devices is an ongoing traffic safety issue. Roadside safety hardware (RSH) is often installed alongside curbed roadways. (The terms “curb” and “curbs” are used herein, respectively, to refer to the presence of any curb and to specific curb-gutter designs.) However, standard, full-scale RSH crash tests do not typically include curb near or around the RSH tested. Although it is generally not recommended to install RSH in combination with curb, it is often necessary to do so along roadways where curb is used. Curb may be added later for a variety of reasons, e.g., to resolve drainage issues, but there are few or no guidelines on placement of the curb relative to the existing RSH.
Previous research examined the effects of curbs in front of longitudinal barriers, but more research is needed on the effects of curbs on the crashworthiness of other RSH, especially guardrail terminals, crash cushions, and breakaway hardware. NCHRP Report 537, Recommended Guidelines for Curb and Curb–Barrier Installations, described the performance of w-beam guardrail installed in combination with curb. Relevant ongoing research is evaluating the effects of curbs on RSH including (a) guardrail terminals, approach guardrail transitions, and Midwest Guardrail System (MGS) studies under the Midwest Roadside Safety Pooled Fund; (b) rigid longitudinal barrier offsets from curb under the Manual for Assessing Safety Hardware (MASH) Implementation (Roadside Safety) Pooled Fund Study; and (c) NCHRP Project 22-39, “Guardrail Performance at Various Offsets from Curb MASH TL-3 Applications.”
Guidelines are needed for the placement of RSH other than w-beam guardrail in combination with curb. Determining the effects of curbs on the crashworthiness of the RSH would provide a measure of assurance in the selection and placement of traffic safety devices and a higher level of safety for the traveling public.
The objectives of this research are the following:
Determine the effects of curbs on the crashworthiness of selected RSH at various speeds, geometries, and offsets from the curb
Develop guidelines for the use of RSH in combination with curb
Prepare the guidelines for incorporation into a future update of the AASHTO Roadside Design Guide
Provide recommendations for any additional crash testing requirements that should be made to MASH on RSH installed in combination with curb
Accomplishment of the project objectives will require at least the following tasks.
Task descriptions are intended to provide a framework for conducting the research. The NCHRP is seeking the insights of proposers on how best to achieve the research objectives. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers’ current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objectives.
Task 1. Review literature and develop a survey on RSH-curb combination performance issues.
Task 1a. Review literature and state-of-practice on RSH used with curbs. Resources should include extant state DOT guidelines on practice, where available, and existing crash data, full-scale crash test data, computer simulations, and in-service performance evaluation (ISPE) data.
Task 1b. Develop a survey for state DOTs and other transportation agencies. The survey shall (a) determine which RSH is most commonly used in combination with curb and, of those combinations, which are the ones with potential crashworthiness issues; (b) what combinations are preferred; and (c) for the RSH-curb combinations discussed, include design speed considerations and data on the curb geometry and location of the RSH in relation to the curb.
Submit a technical memorandum summarizing the findings of Tasks 1a and 1b. NCHRP approval of the technical memorandum and draft survey is required before work on Task 2 may begin.
Task 2. Conduct survey of state transportation and other organizations. Identify which RSH-curb combinations are the most common and potentially critical, e.g., those having crashworthiness concerns. Identify combinations that have been vetted for crashworthiness and could be easily implemented, with or without modifications.
Task 3. Prepare recommendations on which combinations are proposed for further study in the remaining tasks. Include a proposed methodology on how the combinations will be evaluated in subsequent tasks. The research team shall ensure that all barrier products are identified by their design characteristics, not by their brand name or manufacturer.
Task 4. Submit an interim report summarizing the findings of Tasks 1-3. Present findings to NCHRP at an interim meeting. NCHRP approval of the interim report is required before work on remaining tasks may begin.
Task 5. Conduct the approved Task 3 combination evaluation. Results of the evaluation might confirm that (a) use of some RSH devices could be supported by the findings of this study; (b) other devices need crash testing to confirm their suitability for use; and (c) other devices may need modifications for their design or placement under separate research.
Task 6. Develop guidelines and/or best practices for inclusion in the AASHTO Roadside Design Guide and/or MASH. Based on Task 5 findings, prepare draft guidelines for potential implementation by state DOTs, manufacturers, and crash testing laboratories for validating RSH-curb combinations.
Task 7. Submit a technical memorandum covering the findings of Tasks 5 and 6. Present findings to NCHRP at an online or in-person meeting. NCHRP approval of the technical memorandum is required before work on Task 8 may begin.
Task 8. Submit a final report summarizing Tasks 1-7. The final report should including the guidelines and/or best practices developed in Task 6 as an appendix or appendices to the report.
Status: Proposals have been received in response to the RFP. The panel will meet to select a contractor to perform the work.