The NHTSA has promulgated a neu underride regulation (Ref 1) which became effective for heavy commercial trailers manufactured after January 26, 1998. Heavy trucks are excluded. Although this new rule is considered by many to be deficient in some respects (not as good es it could be), it certainly represents a safety improvement over the old FMCSR 393.86, which has been in effect since January 1953 and will continue to be so For heavy trucks. The new rule is also compatible with the European and Japanese rear underride standards.

A series of eight rear underride crash tests (Ref 21, used as a basis For this new rule, demonstrated the effectiveness of en underride guard that minimally complied with the new rule et impact speeds of 30 mile per hour (mph). 6ut in some of the tests the underride magnitude was such that passenger compartment intrusion (PCI) occurred. It has generally been considered that for effective underride performance PC1 should not be alloued. This raises the question:​ hou would this minimally compliant guard (MCG) perform at impact speeds greater than 30 mph which occurs quite frequently in the real world?

This paper addresses this issue based on the previous eight NHTSA underride crash test results. The primary purpose is to illustrate the potential performance of the HCG at impact speeds above 30 mph, end also to demonstrate the effect of guard strength on underride magnitude.