Background Few studies have looked at how obesity affects injury outcomes among vehicle occupants involved in traffic collisions.

Objective To estimate the association of obesity with death risk among drivers of passenger vehicles aged ≥16 and to examine effect modification by driver sex, driver seat belt use, vehicle type and collision type.

Methods We conducted a matched-pair cohort study using data from the Fatality Analysis Reporting System. WHO body mass index (BMI) categories were calculated. Data were analysed using conditional Poisson regression.

Results Estimated risk ratios (RRs) were slightly raised for underweight drivers (RR=1.19, 95% CI 0.86 to 1.63). RR increased with higher BMI categories and were 1.21 (0.98 to 1.49) for BMI 30–34.9, 1.51 (1.10 to 2.08) for BMI 35–39.9 and 1.80 (1.15 to 2.84) for BMI ≥40. Estimated BMI effects varied by gender. We found no meaningful variation across levels of vehicle type, collision type or seat belt use.

Conclusions Findings from this study suggest that obese vehicle drivers are more likely to die from traffic collision-related injuries than non-obese occupants involved in the same collision. Education is needed to improve seat belt use among obese people, as is research to understand the potential role of comorbidities in injury outcomes.