Truck Mounted Attenuator (TMA) is a device that can be attached to a truck for use at worksites to protect road workers from errant vehicle intrusion. All TMAs must be assessed against the Manual for Assessing Safety Hardware (MASH) and approved by the relevant road authority before they can be used on public roads. In Victoria, a list of accepted TMAs can be found in the RDN 06-04.
An important note for TMAs: While heavier support vehicles are likely to have less roll ahead than the tested configuration, the additional mass will increase the transfer of energy into the vehicle occupants during a crash and increase the likelihood of a fatal or serious injury to those road users. The support vehicle mass therefore must be between the minimum and maximum mass limits specified. 

Video Source: Verdegro Group