Here, the only real way to make anything yourself that can be street legal is to make something hover. The traffic laws are only in effect from 0-30 cm (one foot) off the ground, so you can transport your racing machiene on a trailer of some kind. So if you could make something that hovers 31 cm off the ground, no insurance, no lisence and no registration... But any accidents would still cost you billions if you fly into someone without insurance. :p