Tag Archives: coordination

Trying for all-green signals on Highway 305

The in basket:  Dr. Craig Benson writes, “Perhaps you can help me crack the code of the traffic lights along Highway 305 in Poulsbo. I read in the Sun that as part of the revamping of the 305 corridor the lights were supposed to be timed to provide for smoother traffic flow and less stopping, to save gas.

“Since I live off Hostmark and often shop at College Marketplace,” he said, “I have occasion to pass through all six lights in between at various times of the day and night, sometimes with no other traffic interfering, but rarely at rush hours. I’m pretty sure I’ve never made it through all the lights without stopping.

“I’ve tried setting my cruise control right at the posted limit, a little higher, a little lower, accelerating faster and slower from the lights, everything I can think of to pass through the lights as timed, without success.

“This is an every day occurrence for me,” he said, “and probably for hundreds if not thousands of others – those stops add up! Can you find out from the powers that be what I’m supposed to be doing to get through the corridor without making unnecessary and inefficient stops?”

The out basket: The state gets this inquiry enough that it has posted a discussion of the limitations of synchronization on its Web site, at wsdot.wa.gov/Operations/Traffic/Signals/signal_coordination.htm.

After noting that synchronization requires the same number of seconds for each signal to serve all of its various traffic flows,, it poses a question of itself: “Does this mean I will never have to stop for a red light?”


“Unfortunately, the answer to this question is No,” it replies. “There are many reasons why, even when traffic signals are coordinated, you will still have to stop at red lights.”

Among the reasons:

– Pedestrians. Whether those on foot consume some of the time devoted to the various movements  affects the amount of time for other movements.

– Side streets. Even where through traffic is given preference, such as on Highway 305, making for long waits for a green, the goal is to make sure all cars waiting when their queue gets a green light are served. The number of cars crossing affects the main line timing.

– Left turns. The amount of time devoted to them and the number of vehicles waiting to turn subtracts seconds from the main line.

– Two-way traffic flow: Coordinating flows in opposite directions is difficult, especially if the signals in the corridor are spaced differently. “If the spacing is not equal between traffic signals, the green lights may only ‘line up’ well in one direction,” the site says. “When this happens, the green lights will normally ‘line up’ better in the direction with the most traffic. The traffic in the other direction may have to stop.”

– When you drive. Many coordinated system are taken out of synchronization at night and on weekends.

I’ve had to abridge the information on the Web site, for space reasons. Look it up for a more detailed explanation.


Long waits in Kingston during ferry off-loads explained

The in basket Lynn Hammond, who runs a salon in Kingston, wrote in July to ask, “When traveling northbound off the ferry in Kingston and you are stopped at the signal on Lindvog Road turning left, and there are no cars coming toward you going south toward the ferry, why doesn’t the light change for cars to turn left? 

“I know it has to do with the timing of the lights for the off-loading traffic, but if you are in line to turn, it takes forever for the light to change to go left.  The light at the corner of the motel in town has the same problem. I usually experience this in the evening when I am leaving town and there isn’t  a lot of traffic at that time of night.”

She claims to have waited five minutes for the light to change at times and seen exasperated drivers run it. She also told me this week nothing has changed since July.

The out basket: Jim Johnstone of the Olympic Region signal shop says, “During ferry offloads, the signals are in coordination in order to flush the ferry traffic out of Kingston.”

Two possible solutions that might help Lynn are not workable either technologically or for safety reasons, he said. 

Making the outbound left turn light at Lindvog work independently from the rest of the signal to provide just that movement in reaction to a waiting car is beyond that signal’s capabilities, he said. Once it is green, it will stay green until the adjacent through lane has used up its guaranteed 42 seconds of green and turns red, or traffic on Lindvog or the opposite left turn lane is detected. Inbound Highway 104 traffic within the 42-second cycle won’t trip the light, making those drivers wonder the same thing Lynn does about why it takes so long to get a green.

With an average of 470 inbound cars on Highway 104 during the afternoon comparing to only 92 left turners onto Lindvog, more traffic would be disadvantaged by such a change than is now, Jim said. 

Besides, he added, when the system is in coordination, the left turn signal won’t respond to detected traffic.

“It’s a painful lesson we have learned a couple of times,” he said, “including the Highway 303/Bentley (the Wal-Mart) signal (in east Bremerton,) which is not in coordination to allow us to conditionally reserve the left turn into Wal-Mart.”

Allowing left turns whenever incoming or cross-traffic permits, a so-called permissive signal, isn’t a good idea, he said. Once the state decides to allow left turns only when a green arrow permits, it doesn’t want to make the control less restrictive. Their high accident locations tend to be where drivers have the opportunity to turn left when the opposing green light for through traffic also is green, he said.

Kingston’s traffic signals go into coordination whenever a burst of traffic crosses detectors at the ferry terminal during off-loads, he said. The signals then all work on 80-second cycles, of which at least 42 seconds serves the main line. 

So no one should ever have to wait more than 80 seconds for a green light at Lindvog, he said. And an 80-second wait would occur only if the driver arrived at the light just as it goes red for his or her movement.

Outside ferry off-load times, the signals work independently of one another, reacting to the traffic the in-pavement detectors say is waiting.