Question about handicap drivers

I just witnessed something very amazing and extraordinary. I was leaving Matherns awhile ago and this man was in a wheel chair pushing a shopping cart. He only had one arm. Both of his legs and other arm appeared to be amputated. I offered to help him but he declined. I paused to see where he was going. He went to his truck loading his groceries in the back along with his wheelchair. He then got in his truck with a lift device and drove away. Truly amazed at this mans independence. However I'm curious what the rules are governing ones ability to drive a vehicle safely. I just don't see how in an emergency situation he could control the vehicle. Serious question to those that may know.