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Michigan has the highest average car insurance rates in the nation, followed by Louisiana and Oklahoma, according to Insure.com's new national survey of car insurance premiums.

If you live in Vermont or South Carolina, you have access to the most affordable rates, saving $1,000 a year or more compared with drivers in the most expensive states.

Insure.com's study collected auto insurance rates from six large carriers for more than 2,400 vehicles, based on 10 ZIP codes per state. We then calculated averages nationally and for each state.

The reasons for high prices vary considerably among states, but one thing is for sure everywhere: Uninsured drivers are dinging the rest of us.

The big picture

When a state has a large proportion of uninsured drivers, insurance companies aren't able to spread their risk sufficiently. Uninsured drivers aren't paying their share, yet they're still crashing and causing damage, passing the buck to drivers who then make claims on their uninsured/underinsured coverage.

In Oklahoma, 24% of drivers were uninsured in 2007, the fourth-highest rate of uninsured motorists in the country, according to a 2009 study by the Insurance Research Council. Michigan had the ninth-highest rate of uninsured motorists, at 17%, according to the IRC, while Louisiana ranked 27th, with 12% of drivers uninsured.

Despite laws requiring liability insurance in 49 of 50 states -- New Hampshire is the exception -- the numbers of uninsured have likely grown along with the unemployment rate.

"It's more of an economic problem than anything else," says Marc Eagan, the president-elect of Independent Insurance Agents & Brokers of Louisiana, and president of Eagan Insurance Agency in Metairie and LaPlace, La. "They just can't afford the rates."

Michigan car insurance rates pounded by injury costs

The average annual car insurance premium in Michigan increased by $443 from last year's survey, enough for the state to rise from second place to first place and knock Louisiana down to No. 2.

The reason it holds that No.1 spot: Michigan is the only state that guarantees unlimited personal injury protection (PIP) payments to people injured in car accidents. Insurance carriers pay up to $480,000 of PIP benefits; the Michigan Catastrophic Claims Association, a private, nonprofit organization created by state law, reimburses insurers for costs above that amount. Auto insurers also must pay for up to three years of lost wages and replacement services.

Car insurance premiums in Michigan include an annual assessment by the association to pay for medical care when people suffer catastrophic injuries. The assessment through July 30 this year is $143.09 per insured vehicle. And that doesn't include what drivers have to pay for required PIP coverage.

"In some cases, the cost of unlimited medical coverage will be 50% of the entire premium on a vehicle," says Jon Spalding, the president-elect of Michigan Professional Insurance Agents Association and president and CEO of Spalding Insurance Agency in East Lansing and Perry, Mich.

Spalding says Michigan's car insurance law also has some expensive quirks.

Motorcycles are not considered motor vehicles in Michigan, so motorcyclists aren't required to purchase auto insurance -- only minimal liability coverage in case they injure someone or damage property. But as long as they buy the state-required liability amount, they can still collect unlimited medical benefits if they're injured in an accident with a car. In that case, the car driver's policy would pay out first.

"If a high-powered motorcycle ran into me from behind and went over my car, my insurance would provide unlimited medical benefits for the motorcyclist," Spalding says.

While motorcyclists represent about 2% of the assessments paid into the Michigan Catastrophic Claims Association, they account for 7.3% of claims.