Friday, March 16, 2012


Last night in response to a question about roundabouts use to improve U.S. Shelburne Road corridor from om the shopping centers at the I 189 interchange south to the re-constructed roadway to Shelburne, presenter consultant Stephen Rolle paused momentarily and said he was not sure about the safety of the two-lane roundabouts for pedestrians as two-laners would be required to replace the signals.

That question at the Shelburne Road public work session of the Chittenden County Metropolitan Planning Organization (MPO) typifies doubt which still remains about the use on a regular basis of roundabout technology at the busiest intersections. This corridor experienced walker deaths (I dislike the fancied up word “pedestrian”) in recent years and in the 1990s a worker at Price Chopper was killed at the Home Avenue signalized intersection on her way home from work.

For two state transportation agencies (New York since 2005 and Virginia) and two provincial ones north of the border (Alberta and British Columbia) the walker safety issue is “settled” regulation—at busy intersections properly designed and built roundabouts provide, as compared to signals, equal or improved safety for walkers as well as for car occupants and bicyclists.

Per Garder, University of Maine at Orono civil engineering professor and a roundabout expert, circulated a Swedish National Road and Transport Research Instittute (VTI) paper reporting a 1994-1997 thorough study. That study revealed—as do many other studies—single lane roundabouts cut walker injury frequency about 90% and injury severity. There is widespread consensus that single lane roundabouts are the safest intersection treatments period. The two lane roundabouts in the Swedish study also found no problem with two lane roundabout safety—even though the prevalent roundabout designs in place then were larger—about 200 feet in diameter—than current practice--the Federal Highway Administration guidance which is typical calls for two lane roundabouts in urban areas used by walkers to be in the range of 150-180 feet in diameter. These smaller circles mean lower speed, the critical factor in walker crash frequency and severity.
I am in agreement with Professor Garder that two-lane roundabouts pose no safety issue for walkers compared to signals or sign control. To the contrary single lane roundabouts provide a major walker safety benefit and two-lane roundabouts also a positive safety benefit.

Since 1990 when the first modern roundabout was built in the U.S. that number has grown to about 3,000 roundabout today—not a single walker fatality has occurred and the one bicyclist fatality occurred at a very large former rotary with roundabout entries and exits but retaining the higher speed context. Yes fatalities will occur at roundabouts--France with about 31,000 roundabouts records about one walker death per 15,000 roundabouts. A Melbourne statistical report for a five year period last decade found zero walker fatalities in the over 4,000 roundabouts (residential traffic calming circles were included in the overall number).

The Swedish studies of two-lane roundabouts were those with an average of 25,000 daily entering vehicles and 1300 walkers. The translation of the Swedish VTI report published in 2000 concludes its discussion of walker safety findings (emphasis added):

"For the two-lane roundabouts, there is almost perfect agreement between the observed
and predicted values. [“predicted values” were those derived from signalized and
unsignalized accident studies] For the single-lane roundabouts, however, the observed values are substantially (3-4 times) lower than those predicted.
The results suggest that roundabouts pose no problems for pedestrians compared
to “conventional” or signal controlled intersections. The results also clearly
show that for pedestrians single-lane roundabouts are much safer than two-lane

Clearly roundabouts at busy intersections reduce delay for all users, reduce gasoline use and emissions including greenhouse gases (GHGs), cost less to maintain, and overall--and for walkers especially--provide a net safety benefit.

1 comment:

  1. Not a single consideration for roundabout construction on Farrell Street, either.