November 29th, 2010

A METERED APPROACH

Uncategorized, by Catherine Higgins.

Ramp metering has been used during commute times for years, but not all drivers understand why traffic flow is helped when cars stop before getting on the freeway.

Cars stop at 500 South in Davis County, Utah

To non engineers, the concept seems counter-intuitive…UDOT helps traffic mobility by making cars stop briefly before getting on the freeway?

Metering works by breaking up bottlenecks, smoothing out surges and diverting some traffic to other ramps or nearby arterials. In other words, it keeps traffic on an even keel.

In a recent metering study done in the Minneapolis-St. Paul region, the most significant benefit was shown to be travel reliability. Traffic engineers Mark Taylor and John Haigwood explained the results of the study at UDOT’s Engineering Conference.

Some Minnesota law makers decided that ramp metering should be discontinued because of perceived public discontent. The situation provided a good chance to conduct a before and after study of metering.

Reliability is the measure of the expected range of travel times allowing for crashes or excessive congestion. The Minnesota study showed a 91 percent decline in reliability.

Freeway speeds were also much slower. And, traffic volumes were reduced, probably as a result of declined efficiency. ”It was not very long before the public said ‘turn the meters back on,’” said Taylor.

John Haigwood

The study also showed that metering improves safety. Haigwood explained:

– Stop and go driving behavior is reduced, resulting in fewer rear-end collisions.

– Platoons are broken up, resulting in fewer side-swipe collisions.

Metering worked in Minnesota, and it works along the Wasatch Front, too. ”We hear about it when they go off,” says Haigwood. UDOT has studied data to evaluate metering, but has not done a complete before-after study resembling Minnesota’s.

UDOT engineers continually evaluate ramp metering to make sure that commuters see a benefit. “We are trying to help the public the best we can,” said Haigwood.

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