Highway agencies often install safety countermeasures, such as pedestrian and bicycle railings, highway signage, high-protective screening fences, luminaire poles, etc., to the top or backside faces of crash-tested traffic barriers. These features may alter safety performance of the barrier systems. Thus, the Zone-of-Intrusion (ZOI) concept was developed to represent the locations above and behind a barrier system that vehicle components may occupy during an impact event. ZOI envelopes provide guidance for placement of roadside hardware appurtenances above or beyond the face of the barrier.
Current ZOI guidance within the 4th Edition of the AASHTO Roadside Design Guide was developed based on NCHRP Report 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features, TL-2, TL-3, and TL-4 testing. However, AASHTO and FHWA recently agreed to implement the Second Edition of the Manual for Assessing Safety Hardware (MASH) crash testing standard, which utilizes different standardized vehicles, and may significantly change the barrier ZOI. Specifically, the MASH pickup truck, utilized in TL-2 and TL-3 evaluations, has an increased weight and a higher center-of-gravity than the pickup truck used in NCHRP Report 350. Additionally, MASH increased the weight of the single unit truck by 25 percent and increased the impact speed for TL-4 impacts. The increases in weight and impact angle for MASH test 4-12 have also led to an increase in the minimum height to 36 in. for TL-4 barriers. Differences in barrier shape and height may affect the shape of ZOI envelopes. This research provides ZOI envelopes for a variety of rigid barriers under MASH criteria; and a guide for state transportation agency practitioners. The final report NCHRP Research report 1018 : Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments
is available on the webpage.