& s8 f% w. ~+ Y5 i) Y8 x" X+ W* B1 }0 vNew crash tests: Underride guards on most big rigs leave passenger vehicle occupants at risk in certain crashes $ E. q* K% F, r9 \. d7 J% v 8 ?1 F1 G/ W! t3 O5 K# `& KModern semitrailers for the most part do a good job of keeping passenger vehicles from sliding underneath them, greatly increasing the chances of surviving a crash into the back of a large truck, recent tests by the Insurance Institute for Highway Safety (IIHS) show. But in crashes involving only a small portion of the truck's rear, most trailers fail to prevent potentially deadly underride.