Autism is a "broad spectrum" condition - which means it ranges from severe to mild (aspergers).
Aspergers is sometimes known as "high functioning" as those with the condition often have above average intelligence, although they may at first be unable to show it.
My son was born extremely prematurely in 1997, at 24 weeks - so he has always had a high level of clinical monitoring - 56 clinics in the first 12 months of his life!
He continues to have tests for all sorts of things, and only learned to ride a bike (and not very well yet) in 2006.
An investigation into "absence seizures"... which eventually stopped all by themselves.
Simply put, his brain is wired up differently to the norm, so the normal processes of reasoning, dont exist. Instead he experiences input from the various senses, and interprets them and processes them in a different manner. When he experiences too much input, his brain cannot filter the input and prioritise, so it tries to block out some of the input. With Daniel it is sound*.
THAT WILL NEVER CHANGE. Over time however, he will develop strategies to cope with some aspects. He has steered our car while sat on my knee in a large area of private land. I take every opportunity to get him to "drive" - from electric cars, to quadbikes.
Next year I hope to put him in a go kart to learn to recognise control of speed. He needs to develop those skills NOW, before he has to cope with exams, and college or getting a job.
He has already come a long way from this...
He used to watch his feet on the pedals, and exclude looking where he was going - until he hit something!
Now he watches the route ahead, and has a "databank" of hazards in his mind, and will instantly bring the appropriate response into play.
However it is presently limited by experience.
Drivers who have aspergers, or mild autism are just as capable of making competent drivers. The only difference will be the process by which they link what they see, with what they do, and they might not recognise somebody's irate expression if they accidentally cut them up!
*At a guess I would say they would not be able to drive with the radio on in the car, and would meticulously plan a route, and not take any diversion well.