In the 2015 observations, the majority of drivers (73.0%) drove alone, and 22.0% had one passenger in the car. The increase of drivers driving alone since 2014 (4.8%) and the decrease (3.5%) of drivers driving with one passenger is significant (Table 13).
February 1, 2015
Cooper, Jill F; Ragland, David R; Ewald, Katrin; Wasserman, Lisa; & Murphy, Christopher J. (2015). Observational Study of Cell Phone and Texting Use Among California Drivers 2015 and Comparison to 2011 through 2014 Data. UC Berkeley: Safe Transportation Research & Education Center.