What does it take for a car to be classified as street legal?

It depends entirely on the state you will be driving it in.

Nevada?

DOT crash tests and the emissions are two of the biggest things.

For instance, the Mitsubishi Evo was not allowed stateside for a number of years since the intercooler was mounted such that officially “an engine component” was outside the frame of the vehicle. Also, it lacked certain US-required emissions control gear, and adding it resulted in the removal of the AYC (Active Yaw Control) system.

Crash test ratings are also why many electric vehicles are governed to 25MPH and prohibited from many roads. In fact, EVs have confounded some emergency crews since they don’t know the first thing about them. They don’t spill gasoline like normal cars and they have their own special hazards, So how the vehicle is powered also plays a role in it’s legality.

What type of car are you thinking of running in Nevada? That will give me a better idea of what might need to be done. Or are you building your own car from scratch?

Something you may like to consider too..
Finance can be difficult, you could try a personal loan.
Crash safety levels, occupant protection may be inferior to native cars. Insurance can be higher, some insurers may not offer you cover, however, specialist insurers do exist.
The handbook and service history is likely to be in the language of country of origin. The recorded mileage cannot be guaranteed. You won’t have an anti-perforation warranty. Seals and hoses etc will perish faster in differing climates.
The brake balance might feel different. The suspension might feel stiffer. The gearbox ratios might be lower. It may be harder to service and maintain the car, diagnostic equipment may be incompatible making servicing difficult. Some dealers may provide parts and servicing, but check before you buy. Paints and galvanising, particularly on 4×4s, may not be so durable as they’re made for other climates. Repairs may not be easy, The catalytic converter won’t be as effective when run on different fuel. There are no manufacturer’s warranties – although the importer/dealer may offer a mechanical breakdown warranty. It will depreciate more than a native model. You may have trouble reselling privately. :-/ & that’s just in the UK…….

Look at the Department of Motor Vehicles for Nevada requirements

@jerv No vehicle in particular, I was just curious to what some of those aspects make a car not street legal, such as the intercooler in the EVO as you had said.

I recently saw a car from Australia, was right hand drive (which I do not believe that would classify as a car as not street legal), but you could not drive it on the street. It looked like a completely normal car, just wondering what would stop it from being registered.