In one word: Tailored.
That is, the carputer UI is basically first and foremost a relatively big display, which offers a visual interface tailored for the user, it aspires to be neat because it's for the most part designed, trimmed, customized and endlessly tinkered with. The UI grows with the user, as one learns, one modifies. Again and again, if need be. That's why you know your screens better than anything else - isn't that visualization window a bit to the right in the frame? Isn't the media loading slower today?" -, you can tell what's in there at a glance: how's that for interfacing?
Touchscreen comes later, and for those like me who uses steering wheel and/or remote buttons, it's secondary.
The screen is the most important part of the UI, but the customization of course starts much earlier in the choice of a front end, skins, plugins, etc. That means that in the Carputer User Interface everything is tailored for the user by the user, and it just resolves itself in the display.