Changing road design can save gas

He owns a Toyota Prius, gets 44 miles per gallon and can go six weeks without visiting a gas station.

So, what does low-carbon-emitting Alan Falk -- one of The News & Observer's keepers of a weeklong travel diary -- ponder when stuck in traffic?

He wonders how road design could improve fuel economy. Or more precisely, why more fuel-efficient designs haven't replaced traffic signals.

"I hate traffic signals!" he said.

Turns out, Falk, 62, a former electrical engineer, is on to something.

Road design can help reduce congestion. Less congestion means less fuel consumption. Clogged roads contributed to 11.7 million gallons of extra fuel consumed in the Raleigh-Durham area in 2005, according to a recent Texas Transportation Institute report.

Joseph E. Hummer, a civil engineering professor at N.C. State University, said the state has only scratched the surface in exploring the possibilities for unconventional intersection design.

"The eight-phase signal -- it doesn't have to be the way we do intersections," he said.

Hummer said there are as many as 15 tools engineers could choose to design intersections more effectively. Some methods have long been used across the state. Others are just beginning to gain a toehold. Three among those that have won the backing of the N.C. Department of Transportation include traffic signal coordination, roundabouts and "superstreets."

Cut stops, boost mpg

The bottom line: Such techniques reduce the number of stops people make, said Nagui M. Rouphail, director of the Institute for Transportation Research and Education at NCSU. "The highest fuel consumption tends to occur with acceleration," Rouphail said. "As soon as you leave a signal, you accelerate."

Coordinating traffic signals is one of the oldest methods to reduce stops. About half the lights on arterial roads in North Carolina have been coordinated.

The strategy works by sequencing green lights on heavily traveled streets to allow for as much uninterrupted flow of traffic as possible. An NCSU study showed that fuel emissions, which correlate directly with fuel consumption, dropped 10 to 20 percent after signals on Cary's Walnut Street were synchronized seven years ago, Rouphail said.

Chapel Hill, Raleigh and Durham are all in various stages of updating their system of traffic lights, including replacing copper wires with fiber optic cable. The new systems should improve signal coordination and reduce time drivers spend waiting at lights.

But coordination breaks down if signals are spaced more than a half mile apart, Hummer said. Slower drivers fall behind and faster drivers go too fast, so the clumps of traffic become too spread out. This limits the extent signal coordination can be used.

In recent years, roundabouts have grown in popularity. Since 1999, when the state had no roundabouts, the state has put in about 52, said Jim Dunlop, the DOT's congestion management engineer.

Dunlop said he spent nine years at the DOT putting traffic signals in and the past nine years trying to get rid of them all.

Roundabouts are more environmentally friendly than traffic signals because, when navigated properly, they eliminate stopping. Drivers slow down, look for traffic in the circle, then move in.

Roundabouts such as the one Wake Forest installed in 2006 can have aesthetic advantages.

"Roundabouts look better than signals -- the poles, yellow heads and span wire," Dunlop said.

Roundabouts starting

Roundabout construction is also beginning on Eubanks Road in Carrboro. And two roundabouts are headed to Hillsborough Street at Pullen Road and on Oberlin Road in Raleigh, with construction starting around November.

Because roundabouts are not as common in the state as, say, up North or in London, they often face initial resistance.

" 'We're just going to drive round and round like Chevy Chase in "European Vacation," ' " Dunlop said of protests he has heard from opponents. "But once we put them in, most people say: 'When are you going to do this other street?' "

Dunlop also touts another type of intersection design that is catching on: superstreets.

Superstreets have medians that open only one way. In one variation, such as one installed in Chapel Hill in January, drivers who want to turn left continue straight past the [former] four-way intersection, make a U-turn at a cut in the median and then turn right. This way, the busier street gets more green-light time, and traffic flows faster.

"Some of us put our necks on the line" to promote superstreets, Dunlop said.

But judging by the initial success of two that recently opened in Brunswick County and the one in Chapel Hill, the state will probably get more superstreets in coming years. Average travel time through the intersection at Chapel Hill's U.S. 15-501 and Erwin Road-Europa Drive is down about 60 percent, to roughly a minute, Dunlop said.

"We're looking at doing more from the start," he said, "rather than waiting for things to get bad and having to scramble to fix it."