If you go to your local DMV* or your states website you can find out. *department of motor vehicles
This answer will vary state to state, provided you live in the US, for the requirements at your local Department of Motor Vehicles.
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In British Columbia, electric pocket bikes are considered motor vehicles and must comply with the motor vehicle regulations. Generally, pocket bikes do not meet the safety standards required for street use, so it is unlikely that a razor electric pocket bike would be street legal in BC. It's best to check with local authorities for specific regulations in your area.
As a means of transportation, no one may drive a lawnmower on a city street. Lawnmowers cannot be licensed as motor vehicles nor are they equipped with the safety devices required to be on motor vehicles.
To my knowledge, there are no engine size regulations.
Motorcycles are legal motor vehicles and may be operated anytime.
The legal age to ride a motor scooter in Florida is 16. To be eligible, you must have a regular Class E driver license or higher. Scooter must be registered with the Division of Motor Vehicles.
You can visit your local motor vehicle department and request the information that gives you all the requirements needed to make a composite vehicle street legal.
If one is asking about go-karts, they are not street legal. Motor vehicles in Texas are required to have registration and a safety inspection. Safety inspection includes items like; brake lights, headlights, horn, turn signals just to name a few.
A street legal dirt bike is any dirt bike that has a four stroke motor, head lights, brake lights, turning signals, a spark arrestor in the silencer, and street legal on-off road tires.