1967 The National Highway Traffic Safety Administration (NHTSA) of the U.S. Department of Transportation (DOT)issues an Advance Notice of Proposed Rulemaking.

1969 NHTSA issues Notice of Proposed Rulemaking for a rear underride device 18 inches from the ground. Proposed regulation covers most trucks and trailers more than 10,000 lbs. Gross vehicle weight rating(>10K GVWR); agency claims proposal could save up to 100 lives per year; static testing for 75,000 lbs. Centric load capability; no specific design indicated.

1970 NHTSA issues second(revised) Notice of Proposed Rulemaking; guard still would be 18 inches from ground; covers most trucks and trailers >10K GVWR; static test slightly revised and centric load capability lowered to 50,000 lbs.; no specific design indicated.

1971 NHTSA terminates rulemaking.

1977 NHTSA reopens rulemaking with new Advance Notice of Proposed Rulemaking; indicates that tests show that 18-inch-high guard that is energy-absorbing is preferable.

1981 NHTSA issues Proposed Notice of Rulemaking for a device 22 inches from the ground; still acknowledges that energy- absorbing guard is preferable; covers most trucks and trailers >10K GVWR; claims that up to 60 lives per year could be saved; static test revised; centric and extreme offset loads of 11,240 lbs., offset load of22,480 lbs. near horizontal beam/ vertical strut intersection; design specified.

1992 NHTSA issues Supplemental Notice of Proposed Rulemaking for a device maximum 22 inches from ground; again acknowledges superiority of energy-absorbing guard; admits that NHTSA design is only a modification of Interstate Commerce Commission’s guard from early 1950’s; proposed rule now an equipment-standard rather than vehicle-standard; test fixture no longer specified; same centric and offset load capabilities as 1981 proposal.

Proposed rule covers half or less of trailers/ semi-trailers --- all single-unit now exempted; claims that 9 to 19 lives could be saved each year; 776 to 114 non-minor injuries could be prevented; 18 to 27 percent Passenger Car Intrusion underride crashes prevented.