Investigation of Truck Mounted Attenuator (TMA) Crashes in Work Zones in Virginia

About the report:

Truck mounted attenuators (TMAs) are deployed on shadow vehicles in work zones to mitigate the effects of errant vehicles that strike the shadow vehicle, either by smoothly decelerating the vehicle to a stop when hit head-on or by redirecting the errant vehicle. The purpose of this study was to investigate crashes involving TMAs in work zones in Virginia. The objectives of the study were (1) to review trends over the last 3 to 5 years in crashes involving TMAs including a measure of traffic exposure such as the frequency of work zones using TMAs; and (2) to identify the causal factors of crashes in work zones where TMAs are involved.

An email survey of Virginia Department of Transportation (VDOT) and contractor staff was administered to obtain information on the opinions of field forces with regard to the use of TMAs in work zones and their safety in mobile and lane closure operations. Crashes involving TMAs from 2011-2014 in Virginia were compiled and analyzed.

Based on the survey results, driver inattention/behavior, road geometrics/sight distance, mobile operations, and not following the Virginia Work Area Protection Manual are possible contributing factors for TMA crashes. TMA crashes increased from 2011-2014, and most of these crashes occurred on the interstate. A majority of TMA crashes occurred in VDOT’s Northern Virginia, Hampton Roads, and Richmond districts. A typical TMA crash involved a contractor TMA vehicle that was struck from the rear by a male driving a passenger vehicle. TMA crashes accounted for less than 1% of all work zone crashes in Virginia from 2011-2014. There is no clear-cut solution to resolving TMA crashes. Although they represent a small number of crashes compared to the overall number of work zones crashes, most of them affect at least two people: the motorist striking the TMA vehicle and the TMA operator.

The study offers a number of recommendations to reduce the incidence of TMA-involved crashes. First, VDOT should require TMA operator training. Second, VDOT’s Traffic Engineering Division should share the information with regard to TMA crash experience with the VDOT regions, with particular emphasis on the regions with the highest number of crashes. In addition, VDOT’s Traffic Engineering Division should review the benefits of having the first TMA vehicle in a travel lane straddling the lane, as opposed to being fully in the lane, and the spacing of TMA vehicles near ramps during mobile operations. Finally, VDOT should consider working with the Virginia Department of Motor Vehicles and/or others on media and outreach campaigns for distracted driving and include mobile work zones for safer work zones.

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