* The cost of repairing the vehicle following an accident
* The cost of purchasing a new vehicle if it is stolen or damaged beyond economic repair
* Legal liability claims against the driver or owner of the vehicle following the vehicle causing damage or injury to a third party.
Liability insurance covers only the last point, while comprehensive insurance covers all three. Even comprehensive insurance, however, doesn't fully cover the risk associated with buying a new car. Due to the sharp decline in value immediately following purchase, there is generally a period in which the remaining car payments exceed the compensation the insurer will pay for a "totaled" (destroyed, or written-off) vehicle. So-called GAP insurance was established in the early 1980's to provide protection to consumers based upon buying and market trends. The escalating price of cars, extended term auto loans, and the increasing popularity of leasing gave birth to GAP protection. GAP waivers provide protection for consumers when a "gap" exists between the actual value of their vehicle and the amount of money owed to the bank or leasing company. In some countries including New Zealand and Australia market structures mean that people are more likely to buy a nearly new car than a new car so this is less of a problem.
In the United States, liability insurance covers claims against the policy holder and generally, any other operator of the insured's vehicle, provided they do not live at the same address as the policy holder and are not specifically excluded on the policy. In the case of those living at the same address, they must specifically be covered on the policy. Thus it is necessary for example, when a family member comes of driving age they must be added on to the policy. Liability insurance generally does not protect the policy holder if they operate any vehicles other than their own. When you drive a vehicle owned by another party, you are covered under that party's policy. Non-owners policies may be offered that would cover an insured on any vehicle they drive. This coverage is available only to those who do not own their own vehicle.
Generally, liability coverage does extend when you rent a car. However, in most cases only liability applies. Any additional coverage, such as comprehensive policies, i.e. "full coverage" may not apply. Full coverage premiums are based on, among other factors, the value of the insured's vehicle. This coverage may not apply to rental cars because the insurance company does not want to assume responsibility for a claim greater than the value of the insured's vehicle, assuming that a rental car may be worth more than the insured's vehicle. Some states, such as Minnesota, may require that it extend to rental cars. Most rental car companies offer insurance to cover damage to the rental vehicle. In some regions, the costs associated with not having access to the vehicle ("Loss of Use") is also covered.
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What is auto insurance? A basic primer on auto insurance.