The effect of passengers on driver-injury severities in single-vehicle crashes: A random parameters heterogeneity-in-means approach

- Effects of the occupants (both driver and passengers) on driver-injury severities are studied.
- A random parameters logit model with heterogeneity in parameter means is used.
- The method accounts for possible heterogeneity in the means of the random parameters.
- Statistically significant differences exist among sub-populations in the presence/absence of passenger(s).

This paper seeks to investigate the effects of passengers on driver-injury severities. Using single-vehicle crashes, a random parameters logit model with heterogeneity in parameter means is estimated to explore the differences in driver-injury severities in three distinct subgroups; vehicles with one occupant (driver-only), vehicles with two occupants (driver and a passenger), and vehicles with three occupants (driver and two passengers). In addition to considering age, gender and the presence of the passenger(s), a wide range of variables that potentially affect driver-injury severity were considered, including weather conditions, roadway characteristics, vehicle characteristics and driver attributes. Estimation results show that both the age and the gender of the passenger(s) significantly affected driver-injury severities. The findings of this research point toward the need to further study the potentially complex interactions between drivers and passengers.