Gadolhadorah,
An entirely electric car might conceivably be able to be programmed to work like a shabbat elevator, i.e. automatically without the occupant having any effect other than increasing the electricity consumption, which is muttar according to many poskim, but an internal combustion engine automatically adjusts to extra weight by increasing the rate and/or size of the internal explosions, and would therefore be assur due to “hav’arah”.
Akupema,
A non-jew driving is considered the person doing the melacha, and therefore getting him to do it is a rabbinical prohibition of amirah le’akum, with its attendant leniencies, but in an automatic machine anything the jew causes it to do is attributed to him (unless it is done via gramah, the parameters of which are subject to much debate).