- The Washington Times - Monday, September 4, 2006

VIRGINIA BEACH — Philip O’Hara has a system for gauging delays at the Hampton Roads Bridge-Tunnel.

When the electronic message signs over Interstate 64 warn of a 10- to 20-minute delay, he multiplies by two.

“When they say it’s a 10-minute delay, they really mean it’s 20. When they say it’s 15, they mean a half-hour or more,” said Mr. O’Hara, a retired insurance executive who lives in Virginia Beach.

Engineers at the Smart Traffic Center in Virginia Beach, where those predictions are generated, acknowledge he has a point.

The center began warning drivers five years ago of impending trouble at regional water crossings, and the engineers acknowledge it’s more art than science.

“It’s a hard nut to crack,” said James E. Mock, operations engineer at the center, the region’s transportation, electronic-nerve hub.

Although some of the country’s leading engineering firms have studied the complexities of people and vehicles, they have not had much success in making predictions.

“They can send people to the moon, but they can’t predict what traffic will be like in an hour,” Mr. Mock said. “It’s one of the biggest challenges in the traffic-management industry.”

Mr. Mock explains the challenge.

“People think this is easy, but how do you account for people who are not paying attention and are slowing down for no reason, or speeding up, or talking on a cell phone, or drinking coffee?” he asked.

The uncertainty in traffic predictions came into focus in July when routine maintenance at the Hampton crossing prompted the customary delay messages on the signs.

The estimates were wildly off the mark. Some motorists took more than an hour to reach the tunnel entrance, though signs warned of far shorter delays.

Mr. Mock said complaints to the Virginia Department of Transportation prompted a review of the formula, and engineers found a glitch.

The software had been written to predict delays based on both lanes being open but heavily congested. In this case, one lane was blocked with maintenance trucks.

“We didn’t have a time-delay message when there was one lane closed for maintenance,” Mr. Mock said.

“The time delays are when there is an accident and when both lanes are open.”

Brian Smith, an associate professor of civil engineering at the University of Virginia, said engineers also contend with limits on technology.

“Ideally you’d like to measure how long it would take one vehicle to go from point A to point B,” he said.

However, Mr. Smith said, most sensors the state transportation department uses in Hampton Roads count only one vehicle at a time.

The department is now sending out workers in trucks to time how long it might take to travel along a given segment of a local interstate during different times of the day.

Other researchers are buying data from private companies such as package delivery firms that regularly track their vehicles’ movements with global positioning equipment.

The technical limitations on the department’s sensors also have resulted in relying a little more on human insight.

“There is some estimating going on,” Mr. Mock said.

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