The driver in a moving vehicle is at rest or in motion relative to the vehicle.

Movement is a change in the position of a body (or its parts) relative to other bodies over time. The driver does not move in any way relative to the car while he is driving it. Let’s say the driver went to the supermarket and it took him 1 hour. And during this hour, his position relative to the car as a whole did not change in any way. The driver moves relative to the ground, together with the car, at its own speed, but relative to the car he is not mobile.