Roundabouts improve traffic flow, result in fewer crashes and lead to a huge drop in mishaps that result in serious injuries or death, according to government studies.

That's good for motorists, but as more roundabouts appear, some wonder if the circular intersections bring comparable benefits for pedestrians and bicyclists, the most vulnerable users of the road.

It's a relevant question, since last year the number of pedestrians killed on the nation's roads tallied 6,283, the most since 1990, according to the National Highway Traffic Safety Administration. The 857 bicyclists killed last year in crashes with motor vehicles also hit a 20-year high, the agency said.

None of that has been lost on officials in Northfield, where planners are making an extra effort to keep pedestrians and cyclists out of harm's way by incorporating an uncommon feature into a roundabout that will be built next year at the intersection of Hwy. 246 and Jefferson Parkway: underpasses for pedestrians and cyclists.

Crosswalks at roundabouts are generally positioned about 20 feet before the intersection so motorists encounter them before entering the circle. In most cases, crosswalks lead to refuge islands, meaning those on foot only have to cross one lane of traffic at a time. With short crossing distances, the odds of collisions decline.

The Federal Highway Administration says there are 40% fewer crashes involving vehicles and pedestrians at intersections with roundabouts than at traditional intersections with stop signs or stop lights.

Still the potential for danger exists. In Northfield, 4,000 vehicles a day pass through the intersection of Hwy. 246 and Jefferson. The intersection, now controlled by a four-way stop, is near three public schools and a neighborhood with lots of walkers. Traffic backups are common, too, especially at school start and dismissal times, said Northfield Public Works Director David Bennett.

"That is one of the primary reasons for the roundabout," he said.

City officials looked at four alternatives that included some with street-level crosswalks and others with tunnels. There have been no serious injuries or fatalities involving pedestrians or bicyclists at roundabouts in Minnesota in the past 10 years, state records show. Northfield planners wanted to keep the streak going and opted to go with the tunnels to keep pedestrians and bicyclists away from traffic.

"The public is getting used to how vehicle traffic works, but there are still unknowns about pedestrian and bike maneuvering [in roundabouts]," said City Administrator Ben Martig. "The only negative is that it costs more."

The tunnels pushed the tab to about $3.3 million, or about $1.4 million more than the option with all street-level crosswalks. The state will cover $1.8 million and Northfield will kick in the rest.

Officials believe the Northfield roundabout will be only the second in the state with tunnels. There's another near East Ridge High School in Woodbury, said Derek Leuer, a traffic engineer with the Minnesota Department of Transportation.

At any roundabout, Leuer said, pedestrians should make eye contact with motorists, look both ways before crossing and wear clothing that increases visibility. Bicyclists can ride through a roundabout in traffic lanes but must follow the same rules as vehicles.

The bottom line at roundabouts is "always proceed with caution," he said.

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