For region's traffic managers, it's all a matter of timing

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by JOE FRYER / KING 5 News

KING5.com

Posted on October 29, 2012 at 10:49 PM

Updated Monday, Oct 29 at 10:57 PM

SEATTLE – In a perfect world, drivers would hit every green light. 

But reality offers a go-and-stop environment filled with red lights and red faces. 

Perhaps nowhere in Seattle is that more apparent than on Mercer Street, where frustrated drivers are inching to and from Interstate 5 on most days. 

“The lights aren’t synced!” yelled Eleashia Conces as she creeps through Mercer after leaving her job in Seattle’s Queen Anne neighborhood. 

It is not just a problem for the Mercer Mess. In 2012, the National Transportation Operations Coalition gave the nation as a whole a grade of "D+" for traffic signal operations. 

It's easy to complain about the lack of green, but it is very difficult time traffic lights. Traffic engineers just cannot give drivers an endless string of green lights because they must account for oncoming traffic, turning traffic and cross traffic. 

Brian Kemper is the signal operations manager for the Seattle Department of Transportation, overseeing all 1,060 of the city’s signals. Despite what many might think, Kemper said he likes doling out “green time.”

“Try to get them through a series of lights without stopping is the basic strategy,” Kemper said.

The city uses different timing strategies for different areas. 

In downtown Seattle, the timing is fixed. That means there are no sensors to detect cars. The lights simply run on a programmed timer based on the time of day, and pedestrians get a walk signal every cycle without needing to push a button. 

The city uses fixed timing downtown because of the high number of pedestrians. It is assumed pedestrians will need to cross at every direction each cycle.

Fixed timing is also found along Broadway in Capitol Hill and in parts of the University District. 

In other parts of town, many of Seattle’s signals react more to what is actually happening. Because these areas tend to have fewer pedestrians, people trying to cross a street must push a button to get a walk sign. At the same time, sensors beneath the road are counting cars to determine whether green lights should be longer or shorter.  A few years ago, along six corridors, the city started installing "responsive" signals, which measure actual traffic conditions and select from 15 different timing plans. 


Major improvements across the lake

Perhaps no signals in Seattle are as nimble and responsive as the new signals popping up in Bellevue. 

Three years ago, Bellevue became the first city in Washington to start installing adaptive traffic lights. Sensors beneath the road count the number of cars that go through a green light during each cycle. That information is then sent to a city hall computer, which crunches the numbers and creates a new timing plan each and every cycle. 

If the computer sees that lanes are not using all of their allotted green time, it will take that time away during the next cycle and either give it to lanes that could use more time or shorten the length of the entire cycle. 

“What we’re trying to do is just not have any wasted green time and be the most efficient we can,” said Mike Whitaker, who works on Bellevue’s traffic signals.

Bellevue’s 6-year transition of about 180 intersections is costing about $4 million and appears to be worth the investment. Along the heart of NE 8th Street, afternoon travel times are down about 40 percent, the city found. 

On busy Factoria Boulevard, the commute time during 5 p.m. and 6 p.m. dropped by 36 percent. 

“It’s making a huge difference,” said Mark Poch, the city’s traffic engineering manager. 

Chris Hunt, who works in Bellevue, said he has noticed a decrease in his “red time” while leaving work. 

“Traffic seems to be flowing better,” Hunt said.  “There’s not as many cars waiting in line to get out.”

Will Seattle get adaptive lights?

Seattle currently has no adaptive lights, but Kemper said the city could start introducing them in a couple years.  Mercer is a possible candidate, but the lights will first go along Alaskan Way.   

One benefit is that the city would not have to re-time -- or optimize -- its lights as often because adaptive lights are essentially always re-timing themselves. 

Seattle currently re-times most of its signals every five to six years, but would prefer to do it every three years. 

"We know that we can use some more staff to do this, but we’re going to do the best we can,” Kemper said. 

Past Seattle mayors were vocal about traffic signals. Paul Schell ran on a signal-syncing platform, saying in 1998: “God, if we could send somebody to the moon, we certainly ought to be able to synchronize our traffic lights.”

Mayor Greg Nickels spent about $300,000 to sync every downtown light, a project that wrapped up in 2008. 

But budgets for many cities have changed since then. 

“And so you’ve got to find a place to cut,” said expert Ted Trepanier, who works for traffic data company INRIX.  “And so traffic signal retiming work can be one of those things that gets cut.”

Seattle Mayor Mike McGinn is proposing to put about $14 million toward traffic signals in the next couple years. 

Other traffic tools

Seattle is taking advantage of another tool: Special signals that give buses a green light before other cars. 

“If you want to encourage people to ride the bus, you want the bus to go as quickly as possible because a full bus takes 30 to 40 cars off the road,” said Mark Hallenbeck, executive director of the Washington State Transportation Center at the University of Washington.

Bellevue is installing more flashing yellow arrows, giving drivers more opportunities to make left turns, instead of sitting at red lights. 

“Good move,” said Bellevue commuter Chris Hunt. “Thanks, Bellevue.”

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