Greener Driving with Roundabouts

October 1, 2007

Last week, I attended a driving event at the GM Proving Ground in Milford MI. Driving through the campus, there were several places where roads converged at roundabouts (sometimes also known as rotaries) rather than intersections with stop signs. (I’ll have more to say about the content of that event later.) But even before I arrived, I had gone through a couple more roundabouts on the roads in Milford, MI, where GM’s Proving Ground is located. That started me thinking about roundabouts, and how they are greener than standard intersections.

A modern roundabout … is a circle “designed for very low traffic speeds, about 15 mph.” Entrances and exits are curved so that motorists must travel slowly — far different from the rotaries of decades ago, which typically allowed drivers to enter at 35 mph or faster. The Institute says a modern roundabout typically needs to be about 100 feet across so that it can be properly designed to slow the entering traffic. (New Urban News)

Because the traffic only needs to slow down rather than stopping, all the cars traveling through a roundabout avoid the stop-and-go of a stop sign or a red light. Collectively, this adds up to thousands of gallons of fuel saved for each intersection. Avoiding a full stop also allows each driver to get through the intersection faster, which helps make overall travel times shorter.

Roundabouts also help with improving air quality. A study conducted by Kansas State University found

a 38-45 percent decrease in Carbon Monoxide emissions, a 55-61 percent decrease in Carbon Dioxide emissions, a 44-51 percent decrease in Nitrogen Oxides, and a 62-68 percent decrease in Hydrocarbons. Other compiled studies found that when conventional intersections (signalized and unsignalized) are converted to modern roundabouts, there is an average reduction of 30 percent in carbon monoxide and nitrogen oxides, and a 30 percent reduction in fuel consumption.

Roundabouts are also much safer intersections than standard four-way intersections, with some surprising statistics. In a study by the Insurance Institute for Highway Safety, looking at 24 intersections that had been converted from stop signs or traffic signals between 1992 and 1997, overall vehicle accidents were down by 39%, accidents resulting ininjuries were down by 76%, and fatal accidents were down by 90%. Reducing the toll on equipment and hospital services use must also count for a green contribution.

A new pair of roundabouts has been put in at a highway exit in my town near the site of the new high school which is currently under construction. There has been lots of public complaint about it. Some of the criticism is undoubtedly from people who are simply upset with something new and unfamiliar. Concerns have been raised about having the "newfangled" traffic control right in the vicinity of the school, where young, inexperienced drivers will be driving through it regularly. But to my mind, that is the best possible place for it, because those young drivers will quickly learn how to properly navigate a roundabout, and will be less afraid of the new than their elders.

Roundabouts take more space than a standard intersection, so they are less well suited to close urban conditions. They aren’t the appropriate solution for all intersections. Retrofitting existing intersections is not inexpensive, and might not pay for itself for years. But the benefits of roundabouts should be more widely recognized. They are an appropriate solution to traffic management that makes sense from a variety of perspectives.

Image Source: RoundaboutsUSA