Crash Investigation

Best Practice for Truck Mounted Attenuators

Recent crash events involving truck-mounted attenuators (TMAs) in New Zealand prompted an industry-wide study into driver perception of, and reaction to, attenuator vehicles operating in work zones. As an indication of the size and the extent of the problem, the major contractors reported 39 TMA incidents in a 5-year period (1999-2004), including 4 fatalities. The research focused on mobile closures, the primary contributor to the above statistics, and consisted of two consecutive studies. The first study recorded and analysed driver reaction to a range of visual enhancement systems (VES) mounted on attenuator vehicles in a live operating environment during day and night. The second study incorporates the most effective TMA practices from the first study and compared with a new VES, incorporating a mobile advance warning system and European-style board employed overseas.

Significant differences in performance were noted between the different visual enhancement systems, highlighting that an advanced warning system to be implemented above the current standard. A mobile sign, situated in the road's shoulder and forewarning drivers that the lane will be closing up ahead, must be simple to understand and be equipped with flashing strobe lights to attract driver attention. Additional flashing strobe lights mounted above the arrow board, and retro-reflective tape attached to the arrow board surround of the attenuator vehicle demonstrated enhancement capabilities and outperformed any present practice.

Further research suggested driver recognition and manoeuvrability improves as traffic volumes reduce. During off-peak hours, the merging manoeuvre to the open lane is easier to complete, vehicles do not have to queue behind the TMA, and the traffic stream should flow smoothly.

The current findings serve to illustrate the need of uniformity of the operational and visual TMA issues to a high standard across the industry. It also highlights the most desirable improvements that can be made to VES mounted on TMA, which should decrease the number of incidents and fatalities associated with TMA operations currently occurring on New Zealand roads.

Click here to view  further information on the study. (The report ID number is 301 located under the sub heading Traffic Management)

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