The design and strength of front underrun systems are stipulated by EC Directive 2000/40/EC, which, in addition to specifying geometric requirements regarding the width and height of the underrun protection system, also requires the underrun protection system not to be deformed by more than a specified amount when subjected to a static test force. These systems essentially consist of a bar under the conventional fender that extends across the vehicle's entire width. It is fixed to the truck's chassis and generally concealed by a plastic panel or spoiler.
Rear underrun protection systems
Although a rear underrun protection system on trucks and trailers has been fitted as standard for decades, accidents in which a car runs into the back of a truck often have very serious consequences, including even fatalities.
Directive 70/221/EEC, the original directive covering these systems, was superseded in 2006 by the slightly amended Directive 2006/20/EC. Although the new directive requires double the test forces to be applied at three of the five test points, even these requirements may not bring about much of an improvement in the risk of a truck being underrun from the rear in an accident. Because the test forces merely have to be applied statically rather than under dynamic conditions (i.e. crash conditions), what repeatedly happens in crashes is that the underrun protection guard bolted onto the vehicle chassis is bent or completely ripped off and fails to significantly slow down the car that has collided with it.