[micheljansen]

I came up with a similar solution while doing research on "eyes free touch controls" for a certain multinational engineering and electronics company a few years ago.

We found that these types of control perform well, because they effectively have an infinite surface area, but they are not very intuitive, especially when the number of fingers is used to distinguish between different controls. We ended up settling for slightly less "mystery meat" controls similar to Apple's UIDatePicker, which offer a good compromise between being immediately clear and offering a large initial touch surface (which is all that matters, because as soon as you are scrolling the control, your finger is tracked even if it leaves the component).

Touch screen interfaces still have a long way to go before I consider them safe for use in a car though. I did some testing with an eye tracker as well and found that people still glanced at their hands a lot (even after adding artificial tactile feedback). I wasn't able to account for prolonged exposure / experience in my experiments, so maybe it gets better after training.