In Insure.com's latest analysis, Maine's average annual policy premium is $808. The national average is $1,325.
At the other extreme, Michigan ranks as the most expensive state for the third consecutive year. It has an average annual policy premium of $2,738.
The factors that make Maine the cheapest state include not only the state's relatively few large urban areas — and therefore its relatively light traffic — but also its low percentage of uninsured drivers, 4.7 percent.
Maine ranks No. 2 among states with the lowest number of uninsured drivers. That means the state has more drivers to share the risk pool, which drives down costs.
"When everyone is insured, prices go down," as Insure.com puts it.
In Michigan, high no-fault insurance mandates are largely responsible for the high cost of car insurance.
Lori Conarton of the Insurance Institute of Michigan tells Insure.com: "Michigan auto consumers pay more than most states for car insurance due to the state's high medical mandate. Michigan is the only state in the country that requires auto consumers to purchase unlimited, lifetime medical benefits as part of the auto insurance policy."
Insure.com's rankings are based on an analysis of car insurance rates from six large carriers in 10 ZIP codes per state. The rates are based on full coverage for:
A single, 40-year-old male who commutes 12 miles to work each day.
A policy with limits of $100,000 for injury liability for one person, $300,000 for all injuries and $50,000 for property damage in an accident, plus a $500 deductible on collision and comprehensive coverage.
Based on that analysis, the most expensive states are:
Michigan: $2,738 premium
New Jersey: $1,905
Washington, D.C.: $1,773
Rhode Island: $1,608
The least expensive states are:
Maine: $808 premium
New Hampshire: $941
North Carolina: $987
You can find the full rankings at Insure.com.
RELATED: View photos of Google's self-driving cars
Self-driving cars, Google, Tesla
The 10 most and least costly states for car insurance
Google's new self-driving prototype car drives around a parking lot during a demonstration at Google campus on Wednesday, May 13, 2015, in Mountain View, Calif. (AP Photo/Tony Avelar)
Shown is the dashboard of Daimler's Freightliner Inspiration self-driving truck Wednesday, May 6, 2015, in Las Vegas. Although much attention has been paid to autonomous vehicles being developed by Google and traditional car companies, Daimler believes that automated tractor-trailers will be rolling along highways before self-driving cars are cruising around the suburbs. (AP Photo/John Locher)
Brazil's President Dilma Rousseff (L) takes a ride in a self-driving car at Google headquarters in Mountain View, California on Wednesday, July 01, 2015.AFP PHOTO/JOSH EDELSON (Photo credit should read Josh Edelson/AFP/Getty Images)
An Autopilot self-driving sign sits on the window of a Tesla Motors Inc. electric automobile store in Munich, Germany, on Monday, March 30, 2015. Chief Executive Officer Elon Musk wants to transform Tesla into more of a mass-market automaker by building a battery-cell factory big enough to supply 500,000 vehicles by 2020. Photographer: Krisztian Bocsi/Bloomberg via Getty Images
FILE - In this Sept. 25, 2012, file photo, California Gov. Jerry Brown, front left, rides in a driverless car to a bill signing at Google headquarters in Mountain View, Calif. California state officials on Thursday, June 18, 2015 released reports detailing six accidents that involved self-driving car prototypes, reversing a policy that had shielded details of how the next-generation technology is performing during testing on public roads. (AP Photo/Eric Risberg, File)
A Tesla Motors Inc. Model S electric automobile fitted with Robert Bosch GmbH automated driving technology drives on a test track in Boxberg, Germany, on Tuesday, May 19, 2015. The market for automated-driving systems might total $42 billion by 2025, Boston Consulting Group estimated in January. Photographer: Krisztian Bocsi/Bloomberg via Getty Images
A GPS driving sensor antennae sits on the back of a Tesla Motors Inc. Model S electric automobile at the Robert Bosch GmbH driverless technology press event in Boxberg, Germany, on Tuesday, May 19, 2015. The market for automated-driving systems might total $42 billion by 2025, Boston Consulting Group estimated in January. Photographer: Krisztian Bocsi/Bloomberg via Getty Images
MOUNTAIN VIEW, CA - FEBRUARY 02: U.S. Transportation Secretary Anthony Foxx inspects a Google self-driving car at the Google headquarters on February 2, 2015 in Mountain View, California. U.S. Transportation Secretary Anthony Foxx joined Google Chairman Eric Schmidt for a fireside chat where he unveiled Beyond Traffic, a new analysis from the U.S. Department of Transportation that anticipates the trends and choices facing our transportation system over the next three decades. (Photo by Justin Sullivan/Getty Images)
A camera peers out from the front grill of Google's self-driving car in Mountain View, California, on May 13, 2014. A white Lexus cruised along a road near the Google campus, braking for pedestrians and scooting over in its lane to give bicyclists ample space. AFP PHOTO/Glenn CHAPMAN (Photo credit should read GLENN CHAPMAN/AFP/Getty Images)
MOUNTAIN VIEW, CA - SEPTEMBER 25: People look at camera on top of a Google self-driving car at the Google headquarters on September 25, 2012 in Mountain View, California. California Gov. Jerry Brown signed State Senate Bill 1298 that allows driverless cars to operate on public roads for testing purposes. The bill also calls for the Department of Motor Vehicles to adopt regulations that govern licensing, bonding, testing and operation of the driverless vehicles before January 2015. (Photo by Justin Sullivan/Getty Images)
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