Commuting 101: Roundabouts

In The Art of War, Sun Tzu advises you to “know your enemy.” I’m not saying that motorists are a cyclist’s enemy (though some of you would disagree,) but I am saying it helps to think like a motorist at times. Back in 2000 a group of researchers studied how motorists interact with cyclists at roundabouts in Finland, Sweden and Denmark. The study used a “stunt cyclist” and hidden cameras to see how drivers reacted to a cyclists presence. I found the study pretty fascinating and you can read the whole thing HERE.

OP Roundabout

“The most frequent bicycle accident type at roundabouts has been shown to be between the entering driver and the circulating cyclist.” That has been my experience. I used to ride a route that included the roundabout pictured above and it was always an adventure. I pulled up and if there was any traffic coming around the circle my way I would just wait until it was clear. The danger now became inattentive drivers pulling up for their turn, who could be looking right at you and not see you…

I’ve had a few discussions with my brother about this and he has given me his unbiased, expert opinion: if there is a crosswalk available, use it. Let me back track a moment and say that my brother is a former bureau chief for the Kansas Department of Transportation and was kinda the guy who brought roundabouts to the state. He has done a ton of research and is now the engineer that other traffic engineers in the U.S. call on for his expertise on roundabout design. So, I’m not kidding when I say that his is indeed an expert opinion.

He says that when bicyclists share lanes with motorists at a roundabout, they have been proven to be injured at a rate of two to three times greater than at a signalized intersection. He reminds me that the percentage of bicycle accidents are VERY small so an increase of 2 to 3 times is still a small fraction…

Still, he worries about me you see. He did say that roundabouts do slow traffic significantly, which is good in the event of a collision.

Another study states that:

“the difference in speed between cars and bicycles at a conflict point is very important: a reduction in collision speed from 30 mph (48 km/h) to 20 mph (32 km/h) means that the risk of fatal injury is reduced from 45% to 15 or 5% (a factor of 3 or 9).”

The study goes on to say

“The speed through roundabouts is determined by the vehicle path curvature. On single-lane roundabouts, an increase in the vehicle path curvature results in a reduction of vehicular accident exhibits. On multilane roundabouts, however, increasing the vehicle path curvature can result in a higher potential for sideswipe collisions. On double-lane roundabouts, designers are faced with a dilemma: accepting a higher number of sideswipe collisions involving motorized traffic (when they increase vehicle path curvature) or accepting serious accidents involving pedestrians and cyclists (when they decrease
vehicle path curvature).”

So, be aware; your risk of being sideswiped increases when you enter a roundabout. If it is a busy one, and I know this goes against the grain, you may want to heed my brother’s advice and hop off the bike and use the crosswalk … carefully.

Finally, I’ll leave you with some quotes from the Kansas Roundabout Guide:

A bicyclist has a number of options at a roundabout, and your choice will depend on your degree of comfort and experience level with riding in traffic. You can choose to either circulate as a vehicle or use the sidewalk around the roundabout. When circulating as a vehicle, be sure to ride near the middle of the lane so that drivers can see you and will not attempt to pass you.


Well-designed, low-speed, single-lane roundabouts should not present much difficulty to bicyclists. On the approach to the entry, signal your intentions and merge into traffic. It is generally safest for bicyclists to claim the lane. Keep in mind that drivers should be traveling at about 15 to 20 mph [25 to 32 km/h]-close to the speed you ride your bicycle. Most roundabouts will give you three options:

1. Ride like a car: If you are comfortable riding in traffic, ride on the circulatory roadway of the roundabout like a car. Obey all of the same driving instructions as for cars. Watch out for vehicles crossing your path to leave or join the roundabout. Watch out for large vehicles on the roundabout, as they need more space to maneuver.

2. Walk like a pedestrian: If you are uncomfortable riding in traffic and no special separate facility is provided, dismount and exit the approach lane before the splitter island on the approach, and move to the sidewalk. Once on the sidewalk, walk your bicycle like a pedestrian.

3. Use a shared bicycle-pedestrian path: Some roundabouts may have a ramp that leads to a widened sidewalk or a shared bicycle-pedestrian path that runs around the perimeter of the roundabout. Be courteous to pedestrians and yield to them.

I might add to #3 that if there is a bike path at the roundabout, make sure you are riding in the direction of traffic rather than the oposite direction (see the first study mentioned for details).

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