Even a fixed touch UI is dangerous. You can't brace your hand easily to hit a touchscreen and your hand will bounce around while driving. Hitting the wrong button is as or more distracting than having to search for a control. Then there's the shitty UIs with small buttons that are hard to hit accurately even at a dead stop. It seems like every touch screen UI takes all the sins of modern crappy web design and turns it all to 11.

They're just terrible UX for the inside of a vehicle you're driving.