Federal Motor Vehicle Safety Standards (FMVSS) Nos. 223 and 224 require underride guards meeting a strength test on trailers with a GVWR of 10,000 pounds or greater manufactured on or after January 24, 1998. FMVSS No. 224 defines the size requirements for the guards, while FMVSS No. 223 describes strength testing and energy absorption requirements for DOT-compliant guards. This report is a statistical analysis of crash data aimed at determining the effectiveness of FMVSS-compliant underride guards at preventing fatalities and serious injuries in crashes where a passenger vehicle impacts the rear of a tractor-trailer. The primary findings are the following: * Data from Florida and North Carolina showed decreases in fatalities and serious injuries to passenger vehicle occupants when rear-ending a tractor-trailer subsequent to the implementation of FMVSS 223 and 224. However, the observed decreases are not statistically significant at the 0.05 level, possibly due to the small sample sizes of the data. * Using supplemental data collection from North Carolina, it is shown that passenger vehicle passenger compartment intrusion is more apt to occur when the corner of the trailer is impacted, rather than the center of the trailer. This result is statistically significant at the 0.01 level. * It is not possible to establish a nationwide downward trend in fatalities when a passenger vehicle rear-ends a tractor-trailer — neither in terms of total number of fatalities, percentage of fatalities in rear impacts relative to other passenger vehicle fatalities involved in tractor-trailer accidents, nor number of fatal crashes per 1,000 total crashes. The Fatality Analysis Reporting System does not list the model year of the trailer. (Author/publisher)
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