Another possibility...if you want frontal shots of the driver/passenger but don't want to mount a camera outside, mount a mirror on the dashboard on the passenger side of the car then shoot from the back seat into the mirror. Have someone else drive the car while the actor plays the scene in the passenger seat.
You can shoot both characters' angles the same way. Because the mirror flips the image, the driver/actor can just pantomime steering (or pick up a prop steering wheel if you want it in frame). Make sure no large print signs are visible through the car windows as they will be backward.
For the passenger angle, change the background outside and flip the image in post. (You can have signs visible for this one, since it will be flipped.) Best to shoot this on a one-way street so any visible traffic is not in the wrong lane.
For the record, I've never actually done this but I have done many similar tricks using mirrors/flipped images.