Sorry for the late post took a moment to type everything up ::
What you can do is have two objects PlayerCar and Player. For the PlayerCar object you can have a variable boolean instance called 'isDriving' if you player starts out outside of the car then you can set that to 'FALSE' by default. Then if you are using the 8 Direction for control give the car that behavior but again if the Player starts outside of the car set it to 'DISABLED'. Now on you player object create the 8 direction and Pin behavior.
Now in the event sheet you can have when the player is overlapping the PlayerCar and hit whatever key it is to enter the car set the action to 1) Hide the player 2) Pin player to the car 3) set its 8 direction behavior to 'DISABLED' 4)set the car isDriving to 'True' 5)enable 8 Direction. So now where ever the car move to the Player object would follow invisibly.
When they exit the car 1)set car to isDriving 'False' 2)Disable PlayerCar 8 Direction 3) set Player Visible 4)Unpin Player from PlayerCar 5)Set Player 8Direction to 'ENABLED'.
Is another way of doing it. The isDriving boolean can be used in case certain keys match when the player is on foot. So the key would know which to do depending on if isDriving is set to true.