The AASHTO Manual for Assessing Safety Hardware (MASH) test criteria and evaluation thresholds for some tests have historically been conservative to address factors not yet researched and tested, variations between laboratory and field conditions, and other factors. The roadside safety community has been performing research to obtain additional information regarding these criteria and thresholds to determine if current values appropriately account for safety risks to vehicle occupants. Examples include NCHRP Project 17-90 (occupant risk model) and NCHRP Project 22-59 (occupant compartment deformation).
Development of MASH-compliant sign supports, luminaire poles, and work-zone devices has proven difficult due to occupant compartment deformation criteria, roof/windshield/rear window penetrations, and the conservative change in velocity requirements. Evaluation criteria were set low, because of the relative ease in obtaining compliant test results, i.e., low occupant impact velocities and ride-down accelerations, using frangible or slip type bases. The limit from MASH for Occupant Impact Velocity (OIV) is 4.9 m/s for all types of supports. The limit for all other highway safety devices is 12.2 m/s for OIV.
MASH, Appendix Section 2.2.4 notes that, “Energy-absorbing, yielding support structures have been developed as potential replacements for conventional breakaway systems. These devices are designed to decelerate the vehicle to a controlled and safe stop, similar to a crash cushion, rather than permitting the vehicle to break through and continue with minimal reduction in speed…since such a design would not pass occupant risk criteria recommended for breakaway support structures, it should be evaluated according to criteria recommended for a crash cushion.”
Europe has developed a test standard to evaluate supports that utilizes the entire spectrum of device types and occupant risk outcomes: EN12767, Passive Safety of Support Structures for Road Equipment – Requirements and Test Methods. The EN12767 standard for these classes of devices uses different criteria for evaluation that may be applicable here. They have similar impact speeds, three different energy absorption categories, five occupant safety classes, two collapse modes, and two roof indentation categories. EN12767 accommodates the evaluation criteria in MASH but expands on possible outcomes based on support type to produce several different support categories.
The objectives of this research are to (1) compare the MASH test criteria for sign supports, luminaire poles, and work-zone devices to tests for similar devices in the parallel European standard, EN12767, to determine if it may be appropriate to incorporate concepts in EN12767 into MASH, and (2) draft test procedures for AASHTO consideration for potential inclusion into the next version of MASH.
