It's no secret that you're more likely to run into a traffic jam on the highways of a major city than cruising along a rural highway between Midwestern cornfields. And it's intuitive that driving in worse traffic should lead to more accidents — there are just that many more cars to run into.

So in Allstate's new 2008 "America's Best Drivers Report," it's no surprise to see no major American city ranks higher than 10th-safest and a concentration of Midwestern cities populating the top of the leaderboard. But analysis of the report reveals some interesting wrinkles: Low collision rates in your city might not alleviate high insurance premiums and, occasionally, big-city driving might not be much more dangerous than average.

The report declares that overall, the safest city in the United States is Sioux City, S.D., with an average of 14.6 years between collisions. Compare that to the national average of 10.0 years between collisions. Four other Midwestern cities, including three Michigan cities, join Sioux City in the top 10.

Allstate also ranked cities for male and female drivers. The safest male and female drivers are found in Tucson, Ariz., and El Paso, Texas.

In a separate ranking of major cities, classified as those cities with a population over 1 million, Phoenix earned top billing with an average of 9.8 years between collisions. Every single major city had a collision rate above the national average — a disappointing, if unsurprising, statistic.

Phoenix, San Diego and New York were within striking distance of the national average at 1.5 percent, 9.9 percent and 13.2 percent increased risk above the national average, respectively, but the other six cities (Houston, San Antonio, Dallas, Chicago, Los Angeles and Philadelphia) were all above 20 percent increased risk. The bottom line is clear: If you live in a major city, you are at increased risk of a collision.

Another indication of the increased danger of urban driving is that only two major cities appear as safest, while Houston, San Antonio, Dallas, Chicago, Los Angeles and Philadelphia drop off the list.

How do safe drivers ultimately affect your own car insurance? When you live in a town with low accident and car-theft rates, you'll pay relatively less for your car insurance. The Insurance Information Institute (III) publishes the most and least expensive cities in which to insure your car (below), which is interesting in comparison to Allstate's study. The most expensive cities for car insurance, according to III, are all either major cities (Los Angeles, Philadelphia) or urban areas surrounding a major city (Newark and Hempstead, N.Y.), with the notable exception of Detroit, which actually ranked first by a comfortable margin.

Surprisingly, Detroit ranked in Allstate's top 10 safest cities, with a 19.5 percent chance below the national average of a collision. Thus, even if your city is among the least dangerous for collisions, it can still be among the most expensive for insurance. Detroit's insurance rank is pushed up by its high car-theft rate. According to the National Insurance Crime Bureau, Detroit ranks at No. 18 for car theft, with 31,163 cars stolen in 2007.

Other factors that can push up insurance rates in a city are vandalism and fraud. These dangers raise the average policy price as insurers account for claims payments.