Incidence of large truck-passenger vehicle underride crashes in the Fatal Accident Reporting System and the National Accident Sampling System

August 1997

During 1988-93, the Fatal Accident Reporting System (FARS) coded 4% of all fatal large truck-passenger vehicle crashes as involving underride or override (a passenger vehicle going underneath a large truck). In contrast, the National Accident Sampling System Crashworthiness Data System (NASS/CDS) coded 27% of a sample of 275 fatal large truck-passenger vehicle crashes as underrides during the same years. Seven percent of these 275 fatal crashes are identified as underrides in FARS. The discrepancy between FARS and NASS coding becomes more pronounced when underrides involving sides of passenger vehicles or trucks are considered. This is because NASS/CDS did not code underrides involving side impacts, and FARS did. When underrides involving side impacts were added, the total percentage of underrides in NASS/CDS rose from 27% to 50% of fatal truck-car crashes. The most likely explanations for the lower incidence of underride coding in FARS are: (1) The greater amounts of information available to NASS/CDS analysts enable more complete identification of underrides, (2) FARS analysts sometimes may not recognize that underride has occurred, and (3) underride was not a separate FARS variable prior to 1994. Based on NASS/CDS data, an estimated 1,108 fatal underride crashes occurred each year during 1988-93 (95% confidence interval (CI) = 735, 1482). Of these 1,108 underrides, 634 involved the fronts (CI = 328, 942), 248 involved the rears (CI = 137, 360), and 226 involved the sides (CI = 110, 341) of large trucks.