Do your part to prevent distracted driving, even if you're in the passenger seat.
Speak up: If the driver is distracted, say something. It doesn't matter if they're a colleague or supervisor.
Be a copilot: Eliminate distractions for the driver by doing tasks for them. Skip the song, turn up the a/c, send the email — help them out so they can stay focused on the road.
Remember: Be a good backseat driver. Their job is to drive. Yours is to help them do it safely.