Aids for wheelchair to car transfer

I need grips or handles my father can reach and hang-on to while transferring from wheelchair to front seat.

Some cars have hand grips over the door on the inside. Of course, this only helps if you want a new car. If you are looking for handles for a car you now own, that’s different. Which is it?

My uncle is in a wheelchair and drives. When he purchases a new vehicle, he takes it to a company that supplies equipment to those who are physically challenged. And they install grab bars in the vehicle where he can lift himself out of the wheelchair and into the drivers seat.