AASHTO MASH

Abstract

Scope: PURPOSE AND SCOPE The purpose of this manual is to present uniform guidelines for the crash testing of both permanent and temporary highway safety features and recommended evaluation criteria to assess test results. Guidelines are also presented for the in-service evaluation of safety features. These guidelines and criteria, which have evolved over the past 40 years, incorporate current technology and the collective judgment and expertise of professionals in the field of roadside safety design. They provide: (1) a basis on which researchers and user agencies can compare the impact performance merits of candidate safety features, (2) guidance for developers of new safety features, and (3) a basis on which user agencies can formulate performance specifications for safety features. A goal of a highway safety feature is to provide a forgiving roadway and roadside that reduces the risk of a serious crash when a motorist leaves the roadway. The safety goal is met when the feature either contains and redirects the vehicle away from a roadside obstacle, decelerates the vehicle to a safe stop, readily breaks away or fractures or yields, allows a controlled penetration, or is traversable, without causing serious injuries to the vehicle’s occupants or to other motorists, pedestrians, or work zone personnel. Ideally, the roadside would be clear of all obstructions, including unnecessary roadside hardware, and be traversable so that an errant motorist could recover control of the vehicle and stop or return to the travelway. However, there are numerous roadside areas that cannot practically be cleared of all fixed objects or made traversable. At these sites, the use of an appropriate safety feature or safety treatment is intended to reduce the consequences of a departure from the roadway. The crash testing guidelines presented herein cover vehicular tests to evaluate the impact performance of permanent and temporary highway safety features. Performance is evaluated in terms of the risk of injury to occupants of the impacting vehicle, the structural adequacy of the safety feature, the exposure to workers and pedestrians that may be behind a barrier or in the path of debris resulting from impact with a safety feature, and the post-impact behavior of the test vehicle. Other factors that should be evaluated in the design of a safety feature, such as aesthetics, costs (initial and maintenance), and durability (ability to withstand environmental conditions such as freezing and thawing, wind-induced fatigue loading, effects of moisture, ultraviolet radiation, etc.) are not addressed in this document. The procedures described herein include guidelines for direct impact performance evaluation through full-scale crash testing as well as general procedures for evaluating the field performance of a safety feature. New safety features or significant revisions to existing designs should first be evaluated through full-scale crash testing. After a system has been proven to meet the recommended impact performance guidelines, the evaluation should switch to an in-service evaluation of the feature’s field performance. It is recommended that in-service performance evaluations be conducted when new safety features are placed in service. The crash testing guidelines provide a minimum set of requirements that a roadside safety feature has to meet in order to demonstrate its satisfactory impact performance. However, it should be noted that, while these guidelines are representative and applicable to an array of highway features and traffic conditions, they are by no means all-inclusive. Experience has shown that as new designs are developed, current test procedures may not properly evaluate critical conditions for these designs. Experience has also shown that evaluation and testing of features not addressed by the current guidelines will be made. Therefore, specific features and site conditions may arise that require special tests and evaluation criteria. Deviations from the guidelines are warranted when other tests or evaluation criteria are more appropriate and representative of site or design conditions. However, it should also be understood that it is impractical to test a particular feature for all conditions that may be encountered in the field and engineering judgment should be exercised when developing policies for the use of these features under differing conditions. These crash testing and impact performance guidelines supersede those contained in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features (129). Major revisions incorporated herein relative to Report 350 include (a) changes to the test vehicles, (b) changes to the number and impact conditions of the test matrices, (c) changes to the evaluation criteria, and (d) addition of new features to the test guidelines.