Traffic timing challenge goes beyond signals

By Mike Leidemann
Advertiser Transportation Writer

Cheryl Soon, Honolulu's director of transportation services, shakes her head when people ask why the city doesn't synchronize its traffic signals.

At the Honolulu Traffic Management Center near H-1 Freeway, workers are linked to more than 135 traffic cameras around the island and some 400 traffic signals, which can be adjusted as soon as a backup is spotted. Cory Lum • The Honolulu Advertiser

More than 400 of the 1,000 traffic signals on O'ahu are controlled by a central computer system that is routinely tweaked to change the timing sequences at intersections to account for the time of day, heavy traffic, stalled cars, accidents or even an unusually large number of pedestrians.

In recent years, the city has spent millions of dollars to coordinate the timing of signals on every major traffic arterial road in town and as far away as Pearl City and Waipahu. More money is being sought to expand the centralized system to Kane'ohe, Wahiawa and beyond.

Still, people complain.

"Oh, yeah, we hear from them all the time," said Duke Bainum, head of the City Council's Transportation Committee. "A lot of people still think the lights aren't synchronized, but they are. I've been telling them the same thing for at least 14 years."

The problem, city officials say, is that synchronization can only do so much. It can't help when there are more cars going through an intersection than the roads are built to handle.

"It's a matter of capacity, not efficiency," said Don Hamada, chief of the city's traffic signals and technology division.

For many people, synchronization means being able to drive from one end of town to the other with all traffic signals turning green just as they reach them, as if the driver had a magic wand or one of those electronic, remote-control switching gizmos that many emergency services vehicles have.

If all intersections were created equal, that would be relatively simple to do, Hamada said.

The problems come with traffic signals that control more than a simple crossing. In reality, many traffic signals have as many as eight different phases, Hamada said, covering such things as the length of a pedestrian walk signal and left turn lanes for as many as four directions, with differing traffic demands in each direction. When these are timed with less busy intersections along a heavily traveled route such as King Street or Kamehameha Highway, it becomes difficult to synchronize the lights to everyone's satisfaction.

"Two directions, that's easy," Hamada said. "When you go up to eight different phases, things get complicated."

The city's traffic-control system automatically changes the timing on many traffic signals four times a day: morning, midday, afternoon rush hour and night. Officials say their biggest challenge and success in recent years has been developing the ability to change the timing sequences even more frequently, whenever a situation demands it.

The city has installed more than 135 traffic-monitoring cameras around the island, and linked about 400 signals to the central computer and monitoring station in a bunker-like building near H-1 Freeway in Honolulu. The city owns 700 traffic signals and controls another 300 state-owned signals.

As soon as a backup is spotted, traffic controllers have nearly instant ability to dispatch police, roadside assistance, radio warnings and, probably most important, alter traffic lights on nearby roads.

"If an accident occurs on Kapi'olani Boulevard, for instance, we know people will be looking for alternative routes, so we might start lengthening the green lights on King Street or Ala Moana Boulevard," Soon said.

But that works only up to the point where traffic on the cross streets, which now have longer red lights, starts to back up, filling all the available road space between one arterial road and the next.

"Now we've reached the road's capacity, and there's not much more we can do," Hamada said. "It's like putting too much water into a bowl: Eventually it's going to overflow. That's when we start getting a lot of complaints."

It's a challenge in which every second counts. Engineers generally say that for every minute a lane is blocked, cars will back up for 5 minutes. At peak travel times, the delay goes up to 20 minutes. Getting even a few more cars through a busy intersection with each traffic cycle can help cut the congestion and frustration.

One of the most frequent sources of complaint remains the Nimitz Highway area in Honolulu, where a lack of left-turn lanes and heavily used cross streets limit the ability to keep traffic running smoothly. Other problem areas include Kamehameha Highway, Moanalua Road and major shopping centers.

Before the city began centralizing the computer system in 1998, any change in the timing of a traffic signal meant identifying the problem by phone or in person, then dispatching a city crew to manually reset the lights from their individual control boxes. That sometimes that took hours, with traffic backing up all the time.

The city still keeps two crews on standby to correct problems in areas that aren't tied to the central computer. Elsewhere, the timing can be changed in seconds.

"It's amazing how much difference that can make," said Danielle Tucker, who has been doing daily traffic updates since February for the Cox radio network from Honolulu's Traffic Management Center, where the traffic cameras are monitored by city officials.

"It's like watching a shock wave roll through town," Tucker said. "First you can see the wave backing up traffic from where the problem begins. Then, when the changes are made, you can see the wave retreating the other way."

One of the latest routes to be synchronized is Fort Weaver Road in 'Ewa. All 10 traffic signals now run on a coordinated time sequence. Even so, officials aren't sure whether the $1 million project, finished in May, will alleviate the stop-and-go rush hour.

"We haven't had much feedback yet," said Paul Hamamoto, an engineer with the state Transportation Department's Traffic Branch. "It seems to be working, but it's still summer. We'll know better when school traffic starts up again."

City officials say they'd like to see all O'ahu traffic signals linked to the central command post, but that will have to be done in stages.

"It costs $50 per foot to run the network that links the cameras and the lights," Hamada said. "We have to do it a little bit at a time."

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