Massachusetts, besides being the hardest US state to spell, can also boast another dubious honour: it contains both the US’s two most dangerous cities to drive in.

The 10th edition of Allstate insurance’s “Best Drivers Report” surveyed insurance claims from 200 different cities (this year, it took other factors, such as population and weather, into account too). It found that Boston, and the nearby city of Worcester, had the most collisions and worst driving conditions out of the lot.

On average, explained Allstate spokeswoman Kari Mather, a Boston driver will have a collision “every 4.4 years”, which does seem a little high. By contrast, in Fort Collins, the Colorado city which ranked safest in the country, the average driver would expect an accident only every 14.2 years; nationwide, the average is just once a decade.

One explanation, besides things like weather and city size, could be differences in road layout. Fort Collins’ major roads have the classic grid structure, beloved of US city planners and familiar to most drivers:

Boston, on the other hand, has what urban physicists would call an “amorphous” street structure:

And here’s Worcester, MA, which is similarly disordered:

A ranking by author Bert Sperling named Boston as the hardest city in the US to navigate, blaming crowded roads, missing signs, and the sprawling street layout. (This happens in cities that are nearly 400 years old.) On the other hand, a regular grid structure like the one in Fort Collins – a relatively young city, which has grown 10-fold in just 60 years – has less complicated intersections and easier navigation. 

Another factor is the number of intersections per length of road. Civil engineers Norman Garrick and Wesley Marshall researched the issue of Californian street patterns and car safety in 2011. They found that cities with a greater number of intersections actually had less road fatalities overall, as constant intersections make drivers travel at slower speeds and made cycling or walking more appealing. Their research, however, found that both Boston and Worcester had a high volume of intersections, so would receive a high safety rating. Garrick commented that while “fender benders” and other small incidents might have a high incidence in these cities, fatalities and injury levels were low.

Luckily for Bostonian drivers, Allstate doesn’t intend to use the ranking information to determine their insurance premiums.  An interactive map of the data is available here.