Some vehicles are more vulnerable to damage than others because of their lightweight construction and the fact that their crew is exposed to enemy fire. A typical example of an open-topped vehicle is an Ork Wartrak or War Buggy. Whenever a Damage roll (glancing or penetrating) is made against an open-topped vehicle add +1 to the Damage result.
Template and Blast marker weapons are particularly dangerous to open-topped vehicles because their crewmen, wheels, engines and other components are not protected against the flames and shrapnel. To represent this template and Blast marker weapons cause double the normal number of hits against light vehicles (ie two hits instead of one).