Granted a car needs basic equipment, lights, e-brake, windshield etc. I am interested in making a car that will be street legal but NOT modifying an existing vehicle. Also I understand that states vary in some aspects. But I am interested in the basics of what I can get away with making. Like if I make my own car for only MY use (not for general sale or whatever) MUST it have airbags, must it withstand an XX mph collision etc. I can't imagine the car companies can only make a vehicle. I am only interested in 4 wheels and an engine. All the rest can be Mad Max for all I care. The power plant for the engine is not exactly set either. I would like to build it in such a way that I could modify it easily for many experiments, a transmission or gearbox that is easy to work with. There must be a US car law or something website somewhere I am not aware of.