Take the foot rests all the way off of the wheelchair.
Take off the arm rest that is closest to the car and accessories that will be in the way during the transfer.
Park next to a curb so that the wheelchair is at curb's height closer to the level of the car seat. Move the wheelchair next to the vehicle.
Place a plastic bag on the seat that the person is going to be sitting on, and a towel over it. By putting a plastic bag, which is a slick surface, under a towel, which is not, you now have any easy way to slide someone over without giving them a slippery surface to sit directly on top of, which could potentially cause an accident. In addition, the towel provides a grip for you to hold onto to slide them over as well.
Park the wheelchair by the car door and lock the wheels before opening the car door.
While standing between the car door and the wheelchair, with the front of the wheelchair facing the now open doorway of the car, wedge the chair at an angle against the open car door and hold onto the chair handles to keep it stable. Please note that this step will not work with a sliding van door.
If you aren't able to help them move because you're too weak or have other issues that could cause problems while moving them this way, you may wish to consider using a slide board. A slide board is a plastic board that is placed under the person's buttocks and on top of the seat in which the person wishes to sit. The person then slides across the slide board and onto the seat.
Help the person you are transferring find a sturdy grab bar, such as an arm rest or the steering wheel, so that they can push up from the chair, not pull on the door or yourself to get into the vehicle. Assist the person with stepping into or sliding into the vehicle seat with a slide board by providing a stable base for them to hold onto.
If you are using a slide board, remove the arm from the chair on the side in which the person is going to be sliding out. Place the slide board onto the person's seat and the seat they are about to get into. Help them lift their buttocks by tilting to one side, then the other so that they can shimmy onto the slide board. Help them slide over onto the seat and into position.
With the transferred individual now sitting in the car on the towel, go into the vehicle from the opposite door and then grab hold of a corner of the towel and pull it so that the person can be positioned to sit correctly and comfortably on the seat.
Buckle in the safety belt and make sure that the transferred person is comfortable before collapsing their wheelchair and placing it in the trunk of your vehicle.