enlarge Courtesy of Lucy Gibson

This roundabout is one of two built in 2007 in Keene, N.H. Where roundabouts have been installed, motor vehicle crashes have declined by about 40 percent, an insurance group says.

enlarge Gregory Rec/Staff Photographer

Vehicles negotiate a roundabout along the Gorham bypass at the junction of Route 114. Another local roundabout, in Little Falls, has made that intersection safer and eliminated lines of cars at a stop sign, the town’s manager says.

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See multimedia and past stories about Franklin Arterial here.

PORTLAND — How about adding some roundabouts to Franklin Arterial?

That's one of the options under consideration by a city committee looking for ways to slow down vehicles and improve traffic flow.

It's an option that probably will alarm some of the 27,000 motorists who use a portion of the arterial on a typical day. Maneuvering in and out of conventional rotaries and traffic circles can be a bewildering, white-knuckle experience. Moreover, policymakers have found that Americans simply don't like changing their driving habits.

But members of the Franklin Arterial Study Group insist that modern-day roundabouts are completely different from the conventional rotaries that motorists have encountered in Augusta and the Boston area.

Rotaries are designed to enable higher-speed merging and weaving, with vehicles entering the circle having the right of way. But a high number of crashes and congestion problems led to rotaries falling out of public favor after the mid-1950s, according to the Federal Highway Administration.

The modern roundabout was developed when the British redesigned the country's traffic circles in the mid-1960s. These roundabouts are one-fourth the size of typical rotaries and have a tight turning radius and other design features, such as raised splitter islands, that force vehicles to slow down.

The British government also issued a new rule mandating that entering vehicles yield to vehicles already in the circle. By not allowing vehicles to enter until there are sufficient gaps in circulating traffic, the rule prevents circular intersections from "locking up."

The new design's success led to its widespread use in England and its adoption around the world. The first modern roundabout in the United States was built in Las Vegas in 1991. Today, about 1,000 modern roundabouts have been built in 25 states.

New York state has a "roundabout first" policy that requires traffic engineers to first consider the feasibility of building a roundabout before building a signalized intersection.

In Kingston, N.Y., the state built a modern roundabout in the infield of an old traffic circle on the New York Thruway. Although the roundabout drew criticism from motorists after it was built in 2000, it reduced the number of personal-injury accidents by 85 percent in the first year, according to the New York Department of Transportation.

Where roundabouts have been installed, motor vehicle crashes have declined by about 40 percent. Accidents involving injuries have been reduced by 76 percent and fatalities by as much as 90 percent, according to the Insurance Institute for Highway Safety.

Markos Miller, co-chair of the Franklin Arterial Study Group, said he was initially skeptical about roundabouts. But after observing two new roundabouts in Auburn as part of a field trip with a group of city officials, he now views them as an option worth considering.

"The good thing about them is they keep traffic moving, but at a slow pace," he said.

The committee wants to slow traffic in order to make the road less intimidating for pedestrians trying to cross.

Kris Doody, chief executive officer at Cary Medical Center in Caribou, said she has been impressed by the roundabout installed at the intersection of Route 1, North Main Street and the hospital's entrance.

During the 10-year period before the roundabout's completion in 2006, there had been three fatal collisions and numerous near-misses at the intersection, Doody said. Since the roundabout opened, there have been no significant accidents.

"It has proven to be safer than what we had before," she said.

The Maine Department of Transportation also sees the roundabout's benefits. The state is currently completing the conversion of the Cony Circle rotary in Augusta into a roundabout.

Earlier this year in Sanford, motorists began using a new roundabout built at the intersection...