Many people make the mistake of assuming that if their auto insurance policy includes uninsured motorist (UM) coverage, they are completely protected if an uninsured driver crashes into their vehicle. However, standard UM coverage pays only for bodily injury medical expenses that result from an accident caused by an uninsured driver. UM won't pay for your car damage.

If your auto insurance policy includes collision coverage, you don't have to worry. It will pay for your repairs. But you will need to pay your collision deductible. If you don't have collision coverage, you may want to consider a coverage type called uninsured motorist property-damage (UMPD). It pays for repairs to your vehicle if you are struck by an uninsured driver. If you cause an accident yourself, your UMPD does not pay for repairs.

UMPD coverage is generally purchased by drivers who don't have collision coverage. Carrying both UMPD and collision would result in unnecessary redundant coverage — but some states require it.

Industry sources say UMPD is not highly sought-after where it's optional because it applies in only narrow cases: If someone else hits you and they are uninsured.

According to 2008 data collected by the Property Casualty Insurers Association of America, 29 states have laws addressing UMPD coverage. In some states it is required, in others it's optional; some states will automatically include it in your policy, but you may reject it in writing. Because of the wide variations, it's important to consult your insurance agent.

States that do not have legislation addressing the issue do not require UMPD. Depending on your insurer, it may or may not be offered in those states.