Aspects of the present disclosure relate to a vehicle having one or more computing devices that may receive instructions to pick up a passenger at a location, determine when the vehicle is within a first distance of the location, provide a first notification that the vehicle is within the first distance, and stop the vehicle. When the vehicle is stopped, the computing device may initiate a countdown. When a client computing device associated with the passenger has not been authenticated, the computing devices may provide a second notification based on a first amount of time remaining in the countdown and a third notification indicating that the trip is cancelled based on a second amount of time remaining in the countdown less than the first amount of time. Once the third notification is provided, the computing devices move the vehicle from the where the vehicle is stopped without the passenger.