Previous research has indicated that adult drivers are at a lower risk of crashes when accompanied by at least one passenger. One potential reason for this is that passengers can assist drivers on the road via expanding situation awareness, reducing cognitive load and encouraging responsible driving behaviour. Both passengers and drivers report that passengers can be helpful on the road. However, no study has investigated if and how passengers assist adult drivers during everyday driving. The objective of this study was to use passenger and driver conversation to examine ways passengers assist drivers, how what drivers ask for compares to what passengers provide unprompted and how driver and passenger perceptions compare to what actually happens on the road. Twenty drivers aged between 25 and 65 were recruited for this study, along with passengers that they regularly drove with. Participants were recorded completing an on-road navigational task, and subsequently interviewed about their views and experiences with passenger interaction. On the road, passengers did assist drivers by navigating, pointing out hazards, watching for traffic at intersections, expanding the driver’s situation awareness, performing secondary tasks on behalf of drivers and giving feedback or criticism of driver behaviour. While patterns of assistance varied over different driver-passenger pairs, passengers initiated a higher proportion of assistance on average than drivers. During the interview, participants identified that passenger assistance is highly dependent on contextual factors. Participants discussed several ways that passengers assist drivers during everyday driving including increasing driver situation awareness, keeping the driver awake and alert, encouraging responsible behaviour and performing secondary tasks on the driver’s behalf. This is the first study to demonstrate the various ways that passengers assist adult drivers on the road. Passenger assistance does occur during everyday driving and can help to explain the reduction in crash risk associated with driving with a passenger. Further exploration of these findings could further increase our understanding of how passengers assist drivers, what forms of assistance are beneficial and how passengers can be encouraged to be better co-drivers and increase road safety.