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
STATUS: Research in progress.