A truck-mounted attenuator or TMA is designed to protect a road crew working on a road with active lanes of traffic by absorbing the energy of any vehicles which inadvertently enter the work zone and crash into it. The idea is that the TMA should first act as a warning device, which is why most TMAs are fitted with bright lights and high visibility paint. Secondly, the TMA is designed to crumple and absorb the shock of an impact and prevent any vehicle from reaching the crew who are at work in the road.
