When a passenger vehicle collides with the rear end or side of trucks, trailers or buses not equipped with effective guards (bumpers), it continues to travel beneath the taller chassis of the larger vehicle, the passenger vehicle "ride under" the larger one. Therefore, it is important task for us to provide a strong underride protection with low structural weight in order to additionally reduce fuel consumption. This new concept of underride is to introduce polymeric foam into the structures. According to previous research conducted by the author, it is found that by filling the foam into the structures, it is capable to absorb impact energy during the vehicle accident effectively.