Despite mandatory liability insurance laws in 47 out of 50 states, the Insurance Research Council estimates the uninsured motorist rate at about 14 percent nationally and possibly as high as 30 percent in some states. The Property/Casualty Insurers Association of America reports that uninsured motorists are involved in more than 20 percent of fatal crashes in the United States.

But, uninsured drivers aren’t the only problem. Many drivers who have insurance carry only the minimum limits, which may be insufficient to cover all damages in an accident for which they're at fault.

So what happens if you find yourself involved in a car accident caused by one of these uninsured or underinsured motorists? It could be a financially devastating experience unless you have Uninsured/Underinsured Motorist (UM/UIM) coverage.

While UM/UIM coverage is not required in most states, you need this coverage because if you are involved in an accident caused by someone else, and they don’t have the insurance to cover the damage, you can file a claim with your insurer. This is an important safeguard because a motorist who is uninsured or underinsured probably doesn’t have the financial means to pay for any damages resulting from an accident.

Before you purchase Uninsured/Underinsured Motorist coverage, it is important to understand what is covered. Uninsured Motorist insurance (UM) pays for medical expenses, lost wages, and pain and suffering that result from an accident caused by an uninsured driver. UM insurance also protects you and your passengers if a hit-and-run driver strikes you. In addition, policyholders are covered for medical expenses and lost wages if they are hit as a pedestrian, cyclist or commuter.

Underinsured Motorist insurance (UIM) pays for these same expenses that result from an accident caused by a driver who lacks sufficient insurance to cover all of the costs. In some states, Underinsured Motorist coverage is included in your Uninsured Motorist insurance.

Insurers operating in most states also offer Uninsured/Underinsured Motorist Property Damage insurance (UMPD). Whereas, UM/UIM coverage pays for bodily injuries, this coverage pays for damage an uninsured or underinsured driver causes to your vehicle. Covered property may also include personal property inside the vehicle, depending on the state.