What's the best way to keep your rates down? A clean nose.

Maintain a clean driving record. Don't be a speed demon. Don't drive like a maniac. And certainly don't drive while under the influence of alcohol.

That's the conventional wisdom. And it's wise advice, for a number of reasons, including safety – both yours and that of others.

Your own driving record, however, isn't always the biggest factor in determining your insurance rates. There are other factors that are beyond your control, such as your address.

One major factor that determines insurance premiums is geography. It's a fact of life that auto insurance is more expensive in some states than others. To underscore that, Insure.com, in mid-March (March 14, specifically), released its annual national insurance-rate survey, which ranked all 50 states, plus the District of Columbia, by auto-insurance rates.

Do you live in one the priciest states? Well, you do if you live in Michigan, Louisiana, Oklahoma, Montana or Washington, D.C. (Yes, we know, D.C. is not technically a state, but it was included in the survey, which it should be.)

Those are the five priciest states, according to the survey, which was conducted in December by Quadrant Information Services on behalf of Insure.com. The rates are based on a 40-year-old single, male driver who commutes 12 miles to work. The sample policy used in the survey had limits of 100/300/50 ($100,000 for injury liability for one person, $300,000 for all injuries and $50,000 for property damage in an accident), and a $500 deductible on collision and comprehensive coverage. The policy also included uninsured motorist coverage.

You want numbers? Here are those five priciest states with the average annual premium that this representative would pay:

1. Michigan $2,541
2. Louisiana $2,453
3. Oklahoma $2,197
4. Montana $2,190
5. Washington, D.C. $2,146

At the bottom end, the states with the lowest average premiums in the survey were:

47. Tennessee $1,146
48. Wisconsin $1,128
49. Maine $1,126
50. South Carolina $1,095
51. Vermont $995

The national average was $1,561.

See list of all 50 states here.

The rankings were calculated by pricing the policy at six major insurers in each state – State Farm, Progressive, Farmers, Geico, All State and Nationwide, and were adjusted for vehicle type and geographical differences, says Amy Danise, Insure.com's managing editor.

Your own rate would be different, of course, depending on individual circumstances, such as age, driving record, and the specifics of your own coverage.

Differences state to state are accounted for by weather, state insurance laws and the each state's judicial system, says Danise. The reason Michigan is the most expensive, for example, is because it's the only state that guarantees unlimited personal injury protection payments by law, she says. It is also a state that has notoriously poor roads, icy winters and a no-inspection policy, which means that there are some real jalopies running around that can cause accidents for other vehicles.

"In most states, if a person buys injury protection coverage, they can choose their own limits, and your price is based on that," notes Danise. "Most people would choose $1,000, $2,000 or $5,000. But in Michigan, no matter what policy you buy, you get the same unlimited payments, so the insurance company is on the hook for up to $480,000 in personal injury costs, and then anything above that is paid by the Michigan Catastrophic Claims Association.

"So that's very costly for insurance companies." And, of course, those costs get passed on to policy-holders in the form of higher rates.

Lori Conarton, spokesperson for the Insurance Institute of Michigan (IIM), notes: "When people are comparing premiums from state to state, they really need to take a look at the benefits they are paying for those premiums." In Michigan, the coverage also provides for three years of lost wages, survivor benefits and $1 million of property protection coverage. "Michigan's system is really the Cadillac of all auto insurance systems, but it does come at a price."

Conarton says that the IIM supports legislative proposals that would allow drivers to choose the level of medical benefits they need, implement medical fee schedules and initiate anti-fraud programs. "We are hopeful that those reforms can be discussed and debated in Michigan in 2011," she says.

Meanwhile, the reason Louisiana is the second priciest state is because the judicial system generally favors individuals in cases where a policy-holder sues an insurance company – "like, if the company denies your claim for lost wages, or pain and suffering – which can be huge amounts – or if your car is totaled and you don't think you got fair compensation," explains Danise.

States that have a large percentage of uninsured motorists also tend to have higher rates. "If a person with no insurance gets into a crash and causes damage, those who do have insurance have to make the claim," Danise points out. "And, if a state has a large number of uninsured drivers, that means they have a lot of drivers who are not paying into the system. So, both of those factors means that rates to go up for everyone."

Population size and the resulting level of traffic congestion are also factors. One reason that Vermont is the least expensive state in the survey, says Danise, is because of its small population and its lack of large urban centers (which means less traffic congestion, which generally means fewer accidents.)

"And in states like Vermont, in addition to having small populations, they have long hard winters," notes Danise. "So people tend to drive less."

Of course, other surveys of insurance rates, state by state, have been conducted over the years, and different studies use different methodologies. One, conducted by the National Association of Insurance Commissioners (NAIC) in 2008, was released last year and used a different method of calculating average rates. It took the total amount of premiums paid in each state and divided it by that state's total number of vehicles.

In that survey, the top five priciest states, and the average cost of the policies, were:

1. Louisiana $1,274.55
2. Washington, D.C. $1,262.42
3. New Jersey $1,197.91
4. New York $1,171.97
5. Rhode Island $1,138.63

And in the NAIC survey, the least pricey states, and the average cost of the polices, were:

47. Idaho $674.20
48. South Dakota $651.33
49. North Dakota $643.59
50. Wisconsin $641.18
51. Iowa $616.45