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Tue, Oct. 22

Roundabouts are safer, cheaper to build

Since the Prescott City Council voted to replace the traffic signal at Highway 89 and Willow Lake Road with a new roundabout, there have been several letters criticizing the decision.

My reaction was similar. Why replace a perfectly good traffic signal with an old idea that never seemed to work very well? There had to be some reason, so I trotted over to the Arizona Department of Transportation to see why they would propose such a thing.

Alvin Stump, a development engineer with ADOT, provided a great deal of information.

As you know, traffic circles have been around for many years – at many locations in the U.S., but predominantly in Europe. They work with varying degrees of success, but are better on minor roads with light traffic and slower speeds. Many have been replaced; some are still in use.

The modern roundabout appeared in the U.S. about a dozen years ago. Instead of just being a circle for traffic to drive around and get away from, the new roundabout is a carefully engineered device. Now the center island, the road widths at various places, the barriers that slow and direct the flow of traffic, the striping and signs – all of thesethings are carefully engineered.

Apparently there is no standard roundabout – each is designed for the traffic and land at a specific intersection. Stump says that the first ones in Arizona were not the best design, but ADOT is now using some world class consultants. The one at Willow Lake is engineered for the projected traffic in 2025.

There are several roundabouts now being considered by ADOT for different locations around Arizona. Every time one is proposed, the nearby residents claim that it will slow traffic and cause more accidents. "People don't like something different. It's a challenge to get people to accept the benefits," says ADOT.

So, what are the benefits?

Many statistics are available. (Try "AZ roundabouts" on Google.) The ones that impress me most are from the automobile insurance industry – the people who pay for auto accidents. They report that where roundabouts replaced conventional intersections, there were 39 percent fewer accidents overall, 76 percent fewer injury-causing accidents, and 90 percent fewer fatal accidents. That is impressive.

Stump showed me a video of a large roundabout on the campus of Michigan State University. It handles 40,000 vehicles per day and 7,000 pedestrians. It's been in use about five years, and he says that there has not been a pedestrian accident yet. Amazing!

Before a new roundabout is built, the nearby residents usually oppose the idea about 3 to 1. After it has been in operation for awhile, they usually favor it about 3 to 1.

Roundabouts cost less. The two at Interstate 17 and Happy Valley Road (north of Phoenix) cost $2.2 million, but to accomplish the same thing by widening the overpass and adding signs and signals would have cost $8-$12 million.

With roundabouts a narrower roadway can handle more traffic, which saves the cost of buying right-of-way and widening the existing road as traffic increases. There's no need to "store" cars stopped for red lights because there are no lights – a double saving.

The roundabout speed is 20-25 miles per hour, but traffic flows continuously and all legs operate simultaneously, so the average time to go through is less than for conventional intersections.

Environmentally, there is less noise, less pollution, and reduced fuel consumption.

Now, aren't you glad to know all that?

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