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The National Academies

NCHRP 22-34 [Anticipated]

Determination of Zone of Intrusion Envelopes under MASH Impact Conditions for Barrier Attachments

  Project Data
Source: AASHTO Technical Committee on Roadside Safety
Funds: $400,000
Staff Responsibility: C. Crichton-Sumners
Fiscal Year: 2018

This project has been tentatively selected and a project statement (request for proposals) is expected in November 2017. The project statement will be available on this world wide web site. The problem statement below will be the starting point for a panel of experts to develop the project statement.

Highway agencies are often presented with a need to add attachments, 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. However, attachments such as these have been shown to act as vehicle snagging hazards and ultimately degrade the safety performance of the barrier system. Thus, the Zone-of-Intrusion (ZOI) concept was developed to address this issue. ZOI represents the locations above and behind a barrier system that various vehicle components may occupy during an impact event. ZOI envelopes provide guidance for safe placement of barrier attachments to reduce the risk of vehicle snag on the attachments.

Current ZOI guidance was developed based on existing NCHRP Report 350 TL-2, TL-3, and TL-4 testing. However, AASHTO and FHWA recently agreed to the implementation of the new MASH crash testing standard, and MASH utilizes different standardized vehicles, which may significantly change 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 previous NCHRP Report 350 pickup truck. Additionally, MASH increased the weight of the single unit truck by 25 percent and increased the impact speed for TL-4 impacts. Thus, it is expected that the ZOI envelopes for these vehicles will increase in size under the MASH criteria. The increases in weight and impact angle for MASH test 4-12 has also led to an increase in the minimum height from 32 in. to about 36 in. for TL-4 barriers. Changes to the barrier shape, especially height, will likely have significant effects on the shape of ZOI envelopes for TL-4 barriers. Therefore, a need exists to revisit the ZOI guidance for MASH impact conditions and barriers.

The objective of this research project is to develop ZOI for a variety of rigid barriers under MASH impact conditions. The heights of the barriers will range from 20 in. to 42 in., while the barrier shapes to be evaluated include New Jersey Shape, F-Shape, Single Slope, and Vertical shaped barriers. The ZOI for each barrier geometry will need to be determined for different impact conditions as well, including MASH TL-2, TL-3, and TL-4. ZOI will be developed independently for each combination of barrier shape, barrier height, and MASH test level (impact condition). Thus, guidance shall be provided for specific roadway and barrier conditions, not just a uniform blanket ZOI encompassing a variety of installations.

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