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Road construction and maintenance

Road construction and maintenance

Traffic signals

Getting better performance out of our traffic signals is a high priority, both for Public Works and for the Board of County Councilors. The Traffic Signal Optimization Program allows the county to improve traffic flow and rapidly adjust signals in response to crashes, construction and everyday congestion.


For decades, most traffic signals were governed by a programmed cycle dictating how much time is allotted to red, green and, for some signals, left-turn movements. Magnetic detectors embedded in the pavement also allowed vehicles to “trigger” a cycle change and provided some ability to hold green lights for vehicles.

With new technology, the county is able to enhance those capabilities by adding video and radar detection. Modern signals can use this technology to detect oncoming vehicles and adjust signal timing more efficiently and safely for traffic flow.

The county’s goal is to manage traffic signals as an integrated network, not a collection of individual intersections. With changes recently made to traffic signals, drivers are able to travel on county arterials with minimal delay.


The county already has completed upgrades of traffic signals on Northeast 134th-139th Street in Salmon Creek, along with Northeast 78th Street/Padden Parkway, Northeast 99th Street and Highway 99.

In the first four years of the program, approximately three-fourths of the traffic signals in Clark County have been upgraded. The rest of the traffic signals in the Clark County system are expected to be upgraded in 2015 and 2016. Most of the work has been paid for using federal grants.

Upcoming work

The next group of traffic signals to be upgraded is in the Orchards and Sifton areas. The project to upgrade these signals is in the final design phase, with construction scheduled to begin in mid-2015.

Another intelligent transportation system for Clark County is "Traffic Responsive Incident Management." This project will install computer hardware and software on the county's existing traffic signal system to monitor congestion on Interstate 5 in the Hazel Dell and Salmon Creek areas.

Freeway congestion can cause drivers to divert onto county roads. When this happens, the technology will temporarily adjust signal timing to facilitate movement of this additional traffic. The project also will allow the public to view video from cameras at county traffic signals and "real time" congestion information for roads near traffic signals.

Another project, Signal Timing Evaluation, Verification and Enhancement, will install equipment near county’s traffic signals to record travel times. The project also will allow the county to measure how traffic arrives with respect to the green, yellow and red cycles at traffic signals. This information will allow traffic engineers to improve signal timing and obtain specific effectiveness measures.

Additionally, the county will test adaptive traffic signal technology at several intersections to see if it makes sense to install next generation signal technology in more corridors. Adaptive traffic signals are expensive, and the county needs to evaluate if their cost is worthwhile.

Flashing yellow arrows
A new type of signal is being installed and retrofitted to county traffic signals

Flashing yellow arrows allow drivers to turn turn left after yielding to oncoming traffic, pedestrians and cyclists. Drivers should not creep out into the intersection, but wait behind the white stop line until there is a sufficient gap in oncoming traffic and no pedestrians or cyclists.

Flashing yellow arrows can reduce congestion and prevent traffic from backing up at some intersections.

Report signal concern

If you see a malfunctioning traffic signal, please call our Customer Service lines at (360) 397-2446 or submit an online road maintenance request.


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