The results of full-scale tests that were conducted to establish the upper performance limits of conventional W-beam guardrail and Thrie-beam guardrail systems are described. The tests showed that these conventional guardrail systems cannot safely redirect a 9070-kg (20000-lb) school bus in a 15 deg angle impact at 96.5 km/h (60 mph). The development and evaluation of a modified Thrie-beam guardrail are also described. A series of full-scale tests had demonstrated that the unique feature of this guardrail system, a special 0.36-m (14-in) deep blockout, not only prevents the wheels of mini-compact cars from snagging on the posts but also raises the rail during impact to stably redirect heavier vehicles such as school and intercity buses.