While you can only drive one vehicle at a time, in most states to have all of your cars registered they must also have insurance on them. Personal auto insurance companies do not normally offer one blanket liability policy that you pay for one car but can drive several other cars that you own and have registered due to the fact that each type of car has a different risk factor with the car insurance company.

The rating system of an insurance company differs so if you are placing liability on an older Ford Taurus and also a new Mustang you would pay different rates for each vehicle depending upon the rating system of the insurance company. An older car usually has less safety features while a newer vehicle has more safety features so even for Liability purposes you will already get a different rate for each vehicle. Then other parts of the car are also looked at such as engine type so with the Mustang having a bigger engine the risk factors are different again and thus each car has different premiums for you, even if you only get Liability on the vehicle.

State laws requiring each car you own to be registered and insured is meant to ensure that there is adequate coverage in force on all vehicles. It protects innocent third-parties from Bodily Injury and Property Damage in most states since that is the minimum Liability coverages often required of registered owners.

To that effect, it is a matter of safety and public policy, as any vehicle registered could be driven at any time, or even lent to other licensed drivers or resident relatives. So while you may be only able to drive one vehicle at a time that does not mean you could not allow others to drive one of your vehicles and thus have 2 or more of your vehicles on the roadway at once, each needing insurance on it.

State laws and insurance offerings do differ, in Nevada there is a named operator's type of policy available to some car owners. The NV Department of Insurance explains that an operator’s policy is different from standard liability insurance. This type of auto insurance is intended primarily to serve the needs of some car owners such as fleet owners and automobile collectors.

By Nevada law under an operator’s policy, the number of motor vehicles that the policyholder owns must be greater than the number of persons in his household who possess a driver’s license and each person in his household who has a driver’s license must carry an operator’s policy of liability insurance. This insurance coverage protects the driver, not the car. That is, the driver would be insured no matter what vehicle was driven. This insurance coverage does not cover another person driving your car, either with or without your consent though.

Keep in mind that it is possible in most states to buy what's called "Named Operator" Liability coverage but in these instances it available only to trucking companies and fleet owners as a way to insure drivers. If the driver also happens to own the vehicles, he cannot get that coverage typically.

You mentioned driving a car that is not covered by your insurance policy. If your state requires all vehicles to be registered and furthermore require all registered vehicles to be insured than you cannot just insure one vehicle and drive others that are not insured since you would be ticketed for driving without insurance. Your insurance card would list the vehicle that was covered and when it is not the same as what you were pulled over by law enforcement in they would ticket you for being uninsured. Your insurance from an insured vehicle does not extend to an uninsured vehicle since the insurance company does not have it on your policy and has not been able to rate you on the risks they see associated with this uninsured car.

While you can only drive one vehicle at a time most state laws require all your vehicles to be insured at all times they are registered to ensure that proper Liability coverages are in place when any of the cars are on the roadway. If you do not drive all of your vehicles all the time you may see if there is seasonal registration available in your state so that you can place on some vehicles, for instance a truck you only use during the winter months, so that you can take off the registration and insurance during the time the vehicle would be off the road and stored away from public property.

Your state insurance regulator can give you more information on state laws regarding the insurance requirement and need for each car to be insured. This state agency has a consumer division that responds to questions about insurance laws and the insurance industry so you can try getting information on this topic from your specific state regulator. If you own a fleet of vehicles you can see if there are special insurance options available to you in your state such as what Nevada has in place.