Why not enforced collision detection? Presumably that will prevent more accidents than alerting for speed will.

Most manufacturers seem to have these systems already (even if they're reserved as optional extras / high end models) - and it seems crazy that this wouldn't be the first safety measure to apply.

Edit: Seems this story has been moderated: http://hnrankings.info/19498747/ @dang - any idea why? Seems a few stories about EU regs, but this is focusing on motoring.