Rumors has it that this is not done by Square Enix (which acquired Eidos, the original publisher of Carmageddon). There was an open source game presented a little while ago that won a cease and desist at the time. Maybe they negotiated the rights?
Domain comes up as registered by:
Driving Game IP Ltd (DRIVINGG122)
Homestead Cottage, Caulbourne Lane
Yarmouth, Isle of Wight, PO41 0TZ
Domain name: carmageddon.com