Motorists in Sioux Falls — where the streets are laid out sensibly and the traffic enforcement is strong — are the nation's safest and Midwest cities account for half of those in the top 10, an insurance study shows.

Researchers with Allstate Insurance Co. found that each motorist in this growing city in southeast South Dakota has on average one accident every 14.3 years — 30 percent better than the national rate of one every 10 years.

"I've always known we've had good drivers in our city, but I wasn't sure that we were No. 1," said Doug Barthel, police chief in the community of about 137,000. "So it's great news to hear that."

The report analyzed two years of internal crash data to calculate the chance that drivers in 200 of the nation's most populated cities would be involved in an accident.

Factors likely to have helped push Sioux Falls to the top spot include streets that are laid out logicly and strong traffic enforcement, Barthel said. Last year, Allstate's study ranked Sioux Falls second and Cedar Rapids, Iowa, first.

"If we had wide ranges from one year to the next, then we would have to question whether or not the data was really predictive," said George Ruebenson, Allstate's senior vice president for claims customer service.

Following Sioux Falls on the list were Fort Collins, Colo.; Cedar Rapids, Iowa; Huntsville, Ala.; Chattanooga, Tenn.; Knoxville, Tenn.; Des Moines, Iowa; Milwaukee, Wis.; Colorado Springs, Colo.; and Warren, Mich.

Motorists in Newark, N.J., were most at risk, according to the study, averaging an accident once every five years. Washington, D.C., was second-to-last at 5.1 years.

Boston, Worcester and Springfield in Massachusetts were not included because the company does not write policies in the state.

Drivers in Milwaukee, ranked 22nd in population, are likely to experience a crash once every 12.5 years, the best among cities with between 500,000 and 1 million people. Phoenix ranks the highest for safety among cities with more than 1 million people with a collision likely once every 9.7 years.

Researchers studied about 2 million damage claims defined as any collision resulting in property damage filed between January 2003 and December 2004. That's a broad enough period to limit the influence of external factors such as weather and road construction, researchers said.

A weighted average of the two-year numbers determined the annual percentages.

Bill Hayes, enjoying a warm, sunny day Tuesday as cars cruised Phillips Avenue downtown, said Sioux Falls drivers do well compared to those in larger cities.

Hayes, who used to drive a cab in Madison but now walks or uses the bus to get around, said he's noticed a greater sense of urgency, especially among teenage drivers, as the city has grown.

"You have to get there and get there immediately," he said.

Philip Caine, who delivers arrangements for The Flower Shop on busy 41st Street, said his biggest gripes are young people talking on cellular phones while driving and motorists switching two or three lanes without even looking.

Maneuvering around Sioux Falls has gotten even more difficult since construction season began, he said.

"Everywhere you go, you can't go," Caine said. "There's construction everywhere."

Ruebenson said he doesn't have any specific data on what road construction does to accident rates, but road work usually increases the congestion on other roads. And greater congestion typically leads to more accidents, he said.

Allstate planned to give away a tanker full of gas at a Sioux Falls station Wednesday morning to reward residents for their ranking.