Elements of Sustainable Transportation
Roundabouts
| Current Events | Links |
|
Elements of Sustainable Transportation |
Roundabouts |
A roundabout is a type of circular intersection. Compared to signals, roundabouts move traffic more efficiently, cut down on pollution, reduce the number and severity of accidents, last longer, cost less, and do not rely on electricity for operation. A major benefit to roundabouts is that- by increasing intersection capacity- they prevent the need to widen the entire section of street. In other words, a 2-lane road with roundbouts is often more efficient than a 4-lane road with a traffic signals (because the traffic keeps flowing). |
A Recent study of 24 intersections in the United States that have been changed to roundabout showed an 89% reduction in fatalities and serious injury. The accidents in a roundabout tend to be 'fender benders' compared to the much more severe 'T-bone' accident typical of a signalized intersection. There is one aspect of the report that needs much more discussion and research: the appropriateness of roundabouts in business districts. |
 |
Well-designed roundabouts accommodate all modes of transportation. Notice the painted bikeway slightly separated from the carway. Also notice the truck apron. This apron (the white, mountable curb on the outside of the roundabout) allows the back wheels of large vehicles to track over the roundabout- alleviating the need to create a larger (than necessary) roundabout for the occasional big truck. (Note: there is mounting evidence that separating bicycles and motor vehicles is not necessary with single lane roundabouts, especially if a bike slip is provided.) |
 |
Here is another view of a roundabout, with a visually-separated bikeway. (Again, there may not be a need for bikes/ motor vehicle separation within the roundabout- the separation can create blind spots.) |
Three types of circular intersections |
Traffic circle: primarily used for traffic calming in neighborhoods- to slow down traffic and prevent accidents. |
| Rotaries: large, fast, circular intersections. Traffic entering the circle has right of way (opposite for roundabouts). Rotaries are not recommended because of high-speeds, difficulty in maneuvering, and large space requirements. |
| *Roundabouts*: much smaller than rotaries, contain amenities for bicycles and pedestrians, vehicles in the circle have right of way (over vehicles entering), entering speeds around 15mph- huge potential for replacing or complementing signals. |
Another key area for discussion and research is the interaction between cars, bicycles and pedestrians at roundabouts. Safety can be designed for. But, as far as traffic flow goes, a lot of walkers and cyclists can have the effect of backing up car traffic, in essence 'breaking down the flow' of the roundabout. Interruptions in car flow at roundabouts due to pedestrian and bicycle activity can be good- it slows down traffic and also creates gaps for 'down stream' non-motorized crossings. |
A concept to be explored is hybrid roundabout/ signal systems. The roundabout would manage traffic most of the time. The signal could help manage peak flows, emergency vehicles getting through, and sight-impaired people crossing the intersection. |
Public Attitude Toward Roundabouts |
Attitude |
Before Construction |
After Construction |
| Very Negative Negative Neutral Positive Very Positive |
23% 45% 18% 14% 00% |
00% 00% 27% 41% 32% |
* taken from U.S. Department of Transportation statistics |
 |
This roundabout is wheel chair accessible and includes a bench, landscaping and some kind of monument in the center |
Links: |
In: Is This the End of the Road for Street Lights? Roundabout Study on reducing accidents A newspaper article on Chatanooga roundabouts A newspaper article on Tampa Bay roundabouts |
|
www.alaskaroundabouts.com/case.html www.roundabouts.net www.tfhrc.gov/safety/00068.htm www.ourston.com |
| Current Events | Links |