BACKGROUND

AASHTO’s Manual for Assessing Safety Hardware (MASH, 2016) contains the testing procedures used to evaluate various roadside safety features. MASH testing guidelines were intended to provide consistent and reproducible tests. One significant change in MASH is the use of standardized soil stiffness to provide consistency in the performance of safety barriers embedded in soil.  The development of stiffness criteria was based on testing in various U.S. test facilities utilizing soil criteria described in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features, which did not specify soil types or the optimal hardware installations. The MASH specification for soil stiffness defines a minimum stiffness for the response of a standard W6x16 steel post surrogate to dynamic loads for a specified soil type and correlates this response to a static load test to be performed as part of each soil-based crash test.

Since the implementation of MASH testing, concerns with this new soil stiffness criterion have been noted. The first of these is the lack of a maximum stiffness limit. Highly stiff soils can negatively impact system performance, and there is concern that the lack of an upper stiffness limit does not provide consistent testing between laboratories and various installations. Other potential issues relate to the optimization of the current testing for identifying salient properties of a variety of soils utilized by various crash testing facilities.

Over the past few years, many crash tests have been performed on a variety of systems under MASH criteria. The opportunity to evaluate the efficacy of and potentially improve the new stiffness-based soil criteria is timely and critical to the continued improvement of roadside safety. Since MASH is the standard for evaluation of roadside safety devices, the research could affect state departments of transportation (DOTs) and other transportation agencies. Research is needed to review the current MASH soil specifications and evaluation procedures to ensure consistency in crash testing and develop proposed language for consideration by AASHTO to incorporate the research results in the next update of MASH.

OBJECTIVE

The objective of this research is to evaluate the impact of soil stiffness on the performance of crash testing and roadside safety.

STATUS: Research in progress.