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.

Wednesday, March 14, 2012



The myth of the traffic growth even when it crashes remains a staple mantra of planners and engineers—remember the Circumferential Highway anyone? Burlington (VT) perpetuates the myth in its downtown planning process, PlanBTV. A key base PlanBTV report claims--without providing evidence--that vehicle travel will increase one percent a year for the foreseeable future.

Now a couple of decades ago—the 1980s—found Vermont and New England vehicle travel growth up over 30 percent—but after the 1980s the sharp downtrend started leading to a 3% growth in the first decade of this century with Rhode Island actually turning negative. New England car travel growth even trailed of population growth just over 3%.

Vermonters can reasonably expect vehicle miles of travel turning negative this decade for a number of reasons. Urban Vermont leads the downtrend with then Vermont Agency of Transportation (VAOT) providing a five-year “short term” traffic factor for urban areas for planning purposes—the factor for a decade has remained about 0% change for planning purposes.

Take a closer look at Burlington and you find, for example, that one of the three corridors feeding the downtown, Route 127, the “northern connector” hit its top numbers in 1989 and since then, over two decades, declined steadily averaging -1.1% a year with a daily volume of 14,300 last year, down 21.3% for the period 1989-2011 with both 2010 and 2010 in the negative. No growth here.

How about the southern gateway, Route 7? Route 7 shows minor growth or decline over two decades at the I 189 interchange. And, I 189 itself since 1992 has added a puny few cars annually, averaging an increase on a per decade basis 30 more cars on and 30 more cars off, 0.3% growth per year or a 3% per decade rate of increase. Most of the short road sections around the I 189 interchange on Route 7 peaked about two decades ago. No growth here.

Finally take a close look at three downtown street sections: (1) Main Street from St. Paul Street to Battery Street; (2) Battery South to King Street; and (3) Battery Street north to College Street. Any growth on these three segments? From a base of about 1990 to 2010—two decades—the Main Street section daily numbers dropped 34%, Battery from Main to King down 21%, and Battery Main to College 10%. Really, will the drop in car travel ever stop around here?

It is important to emphasize that even car travel downtrends mean some roads will increase while most decline. For example, several interstate segments which carry about a fifth of all highway traffic statewide do show some growth.

Roundabout Potential

In terms the actual numbers each of the intersections in the downtown—St. Paul/Main Streets, Battery/Main Streets, Battery/King Streets and Battery/College Streets—all have vehicle counts which suggest a single lane roundabout with its safety for walkers can be considered. Single lane roundabouts offer a 90% reduction in walker injuries and about the same benefit to car occupants. The roundabout holds the key to a highway “zero fatality” rate policy which is advocated by AAA since no other technology can reduce speeds along typical streets and highways as well as radically improving safety at intersections. And single lane roundabouts even in the eventuality of increased traffic generally outdo the performance of what really is obsolete technology, traffic signalization.

So when the planners and engineers talk about increased car travel numbers, ask them to provide the data and reasoning that supports their claims.