Belted driver fatalities: Time of death and risk by injury severity

This is a descriptive study of the fatality risk by injury severity and time of death for lap-shoulder-belted drivers without ejection in modern vehicles. It also determined the body region for severe injuries experienced by belted drivers using the most recent federal crash data.

1997-2015 NASS-CDS data were evaluated for fatally injured lap-shoulder-belted drivers without ejection in light vehicles of 1997+ model year (MY). The severity of injuries sustained by belted drivers was assessed by the Maximum Abbreviated Injury Scale (MAIS) and individual injuries by Abbreviated Injury Scale (AIS) and body region. The change in fatality risk with MAIS was fit with a Logist function. Time of death was determined using the variable DEATH, which is reported hourly in unequal intervals up to 24 h and then daily up to 30 days after the crash. The fraction (f) and cumulative fraction (F) of the deaths are reported for each time period up to 30 days. A power or logarithmic curve was fit to the data using the trendline functions in Excel.

The NASS-CDS sample included 20,610,000 belted drivers with 37,974 fatalities from 1997 to 2015. The fraction of driver deaths increased with maximum injury severity (MAIS). For example, 17.4% of drivers died within 30 days with MAIS 4 injury. Virtually all drivers (99.7%) died with MAIS 6 injury. The change in fatality risk with injury severity was r = [1 + exp^{(10.159 - 2.088MAIS)}]^-1, R² = 0.950. Overall, there were 19,772 driver deaths with MAIS 4-6 injury and 13,059 with MAIS 0-3 injury. In addition, 44.7% of driver deaths occurred within 1.5 h of the crash, 56.7% within 2.5 h, and 64.6% within 4.5 h after the crash. The cumulative fraction of the deaths (F) up to 30 days was fit with a logarithmic function. It was F = 0.0739ln(t) + 0.5302, R² = 0.976, for deaths after 3.5 h. There were 19,772 driver deaths with 52,130 AIS 4+ injuries. On average, the driver experienced 2.64 AIS 4+ injuries most commonly to the head (44.5%) and thorax (38.1%).

The risk for belted driver deaths exponentially increased with MAIS. A majority of deaths occurred within 2.5 h of the crash. On average, fatally injured drivers experienced 2.64 AIS 4+ injuries, primarily to the head and thorax.