Recommended Procedures for the Safety Performance Evaluation of Highway Features

TRB's National Cooperative Highway Research Program (NCHRP) Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features presents procedures for conducting vehicle-crash tests and in-service evaluation of roadside safety features or appurtenances including (1) longitudinal barriers such as bridge rails, guardrails, median barriers, transitions, and terminals; (2) crash cushions; (3) breakaway or yielding supports for signs and luminaires; (4) breakaway utility poles; (5) truck-mounted attenuators; and (6) work zone traffic control devices.

The purpose of the procedures is to promote the uniform testing and in-service evaluation of roadside safety features so that highway engineers may confidently compare the safety performance of designs that are tested and evaluated by different agencies. Standardized procedures are presented for the testing and evaluation of features under severe vehicle impact conditions rather than to typical or average highway situations. This report represents a comprehensive update of the procedures for safety performance evaluation described in NCHRP Report 230. The evolution of roadside safety concepts, technology, and practices, significant changes in the vehicle fleet, the emergence of many new barrier designs, increased interest in matching safety performance to levels of roadway utilization, new policies requiring the use of safety belts, and advances in computer simulation and other evaluation methods necessitated an update.

The report differs in the following ways: (1) It is presented as an all metric document; (2) It provides procedures for the testing of a wider range of barriers, terminals, crash cushions, breakaway support structures and utility poles, truck-mounted attenuators, and work zone traffic control devices; (3) It uses a 3/4- ton pickup truck as the standard test vehicle in place of the 4500-lb passenger car; (4) It defines other supplemental test vehicles including a mini-compact passenger car (700 kg), single-unit cargo trucks (8000 kg), and tractor/trailer vehicles (36,000 kg) to provide the basis for optional testing to meet higher performance levels; (5) It includes a broader range of tests for each category of device to provide a uniform basis for establishing warrants for the application of roadside safety hardware considering the levels of utilization of the roadway facility; (6) it includes guidelines for the selection of the critical impact point for crash tests on redirecting-type safety hardware; (7) It provides information related to enhanced measurement techniques related to occupant risk; (8) It retains the three basic evaluation criteria, but alters the limiting values for acceptance; (9) It reflects a critical review of other methods and technologies for safety-performance evaluation, such as surrogate test vehicles and computer simulations, and incorporates state-of-the-art methods in the procedures; and (10) It provides optional criteria for side-impact testing. The evolution of the knowledge of roadside safety and performance evaluations is reflected in this document.