Q: Why do the traffic signals at Fifth Avenue Northwest and the Meridian/Second Street couplet in Puyallup seem so out of synch? – Janet W., Puyallup
A: First, let us set the scene.
The main north-south drag through the heart of Puyallup is the Meridian/Second Street couplet.
Meridian is one-way southbound. Second Street (and sometimes Third Street) is one-way northbound.
Now Fifth Avenue Northwest crosses both stems near Grayland Park.
Got it? Good.
We will let Janet, who frequently drives on Fifth Avenue Northwest, take it from here.
“There is a light for Second and a light for Meridian,” she wrote to Traffic Q&A headquarters. “They are terribly out of synch with each other!!!
Invariably, you are sitting at Second waiting the light to turn green, and the light on Meridian is glowing green with absolutely NO traffic in either direction!!! The same can be true in reverse. You get through Second and have to wait at Meridian for no reason. Is there an explanation?”
We put Janet’s question to Mark Palmer, Puyallup city engineer.
Palmer explained that the signals along the Meridian/Second couplet are controlled by “an adaptive traffic signal system” from 23rd Avenue Southeast to River Road. The system was produced by an outfit called Rhythm Engineering.
“The system optimizes traffic along the preferred corridor by creating what Rhythm refers to as ‘tunnels,’ ” Palmer said. “Depending on the time of day and direction of travel, these tunnels can be up to 120 seconds long.
“Generally speaking, if you entered a corridor at the start of a tunnel and traveled at the design speed (not necessarily the speed limit), you should be able to travel the length of the corridor most times without stopping.”
Now the city can adjust the system for certain scenarios, including ordering signals to shorten, or truncate, themselves if there is no traffic coming from one direction or other.
For example, Palmer said, “If no cars are coming after a percentage of the tunnel time, the system can terminate the tunnel. If truncation is set at 60 percent and the tunnel is at 120 seconds, the tunnel can be truncated at 72 seconds if no cars are coming.”
OK, good general information. But what about Janet’s issue?
“I did just check the truncation on the Fifth/Meridian signal,” Palmer said. “It appears that it is set at 100 percent, so the tunnel is not being truncated at all. That can mean a waits of up to 120 seconds (depending on the time of day) with potentially no cars coming on Meridian.”
Palmer told us the city will lower the truncation percentage at that intersection to address Janet’s complaint. That might not eliminate the wait, but it should shorten it.
In the meantime, Palmer encouraged people with questions or concerns about traffic signals to let the city know.
“ … We do appreciate reports on the system,” he told us. “We do not have staff to monitor it 24/7, so we rely heavily on reports to spot issues. When we do have issues, we will investigate, look at the data the system is providing us, and make adjustments as needed.”
The phone number for City Hall is 253-841-4321.