Three seconds have been missing from Silverdale left turns

The in basket: Byrd Thibodaux and Tom Wisniewski both e-mailed me in June about the short green light they were getting in the double left-turn lane on southbound Silverdale Way to eastbound Bucklin Hill Road.

Byrd estimated it to be three seconds, and said, “In the afternoon, there is quite a line of cars in the two lanes.  With this light only being three seconds, many frustrated drivers continue through the light on red.  Why can’t the county add a couple of more seconds to this light?”

Tom wrote, “You get an arrow long enough for three cars (four if someone runs the yellow/red) before the light goes red.

“I thought a big study was done in Silverdale last year to correct these kind of problems,” he said. “Someone needs to do more studying at this intersection.”

The out basket: I watched that signal in operation three times in the intervening weeks and found that it actually was allowing six seconds of green before going to yellow.

I’m surprised that only Byrd and Tom have complained about it. Tom’s estimate of three or four cars is close. I found that five cars could get through on the green and red combined  – IF none of them dawdle.

Often a lead driver wouldn’t even start forward until two or three seconds of green have elapsed, which could cut the put-through at three. When I watched it on weekday afternoons, many cars that were in the turn pockets when the light changed didn’t get through.

Del Gann of the Kitsap County signal shop said the light was supposed to be providing nine seconds of green. That probably would double the  number of cars getting through.

But even the nine seconds amazed Tom Wisniewski. “NINE SECONDS,” he replied when I told him what Del Gann thought the light was providing for left turners. “They have got to be kidding. This is a major intersection in Silverdale and they think nine seconds is enough time for left turns.”

That’s what the computers said would be appropriate as part of the coordination of all the lights along Silverdale Way, which he reinstated this spring, Del said.

“If the signal is running nine seconds of green time that means that at least 14 seconds is dedicated to that movement after you add in the yellow and red time.  One might then say, well, 14 seconds isn’t a lot of time either, but you have to consider the big picture.

“The corridor is running a 130-second cycle length for coordination. This is what is determined to be the best to optimize the progression of traffic through the corridor. So the 14 seconds is over 10 percent of the total cycle length. (The amount of time the signals can’t be serving other movements)

“To further complicate this the current configuration of the signal serves eastbound separately from westbound and the time dedicated to those movements is dictated by the time needed for pedestrians to cross the street.

“Then finally you have to take into account the volume of traffic that is on Silverdale Way (the coordinated movement) and need to make sure the green time is sufficient.

“When you look at the volumes for the intersection the current timings (considering necessary pedestrian crossing times) allow for the most effective movement through the intersection for all traffic, he said.”

But I finally convinced Del that what he wanted there wasn’t what was happening.

Tuesday he told me he’d watched it do what I said it was doing. “Because of the way the signal is sequenced,” he said, “that phase will be abbreviated if any other runs over at all. That explains why the shorter green is occurring at the busy time of the day.

“I have added three seconds to that movement as a temporary fix so I can bring the intersection into the shop and test it to find out where the error is,” he said. “This will ensure that the movement will get all of the time that is programmed.”