Estimating side underride fatalities using field data

There is evidence that underride events are undercounted by the Fatality Analysis Reporting System (FARS), a census of fatal crashes on public roads in the United States. This study's principal objective was to develop accurate fatality estimates for side underride crashes involving "combination trucks" and light vehicles. Police reports from 29 states were used to estimate the incidence of fatal crashes in which light vehicles underrode the sides of large combination trucks. A protocol was developed to judge the presence of underride with passenger compartment intrusion (PCI), and an in-depth manual review of police reports was performed using scene diagrams, narratives, vehicle and occupant data. The incidence of fatal underride was then compared to that reported in FARS to determine the extent of underreporting in FARS. Further, a comprehensive review of side underride crashes resulting in fatalities and injuries was made using the Large Truck Crash Causation Study (LTCCS) data, the most comprehensive database on large truck crashes. Results show that only a small proportion of the light vehicle occupant fatalities resulting from collisions with combination trucks involve a side underride, and an even smaller proportion involve a side underride with PCI. An in-depth review shows the ratio of underreporting of side underride crashes in FARS is a factor of 3.1 (CI: 2.9-3.3); thus, the annual number of light vehicle side underride fatalities with PCI is estimated to be 202 (CI: 189-215). Comparison of FARS / LTCCS data shows results consistent with this underreporting estimate. LTCCS data also shows that non-fatal serious injuries to light vehicle occupants in side underride crashes involving combination trucks are extremely rare.