Getting better performance out of our traffic signals is a high priority, for Public Works and 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, Highway 99 and throughout the Orchards and Sifton areas.
In the first five years of the program, ninety five percent of the traffic signals in Clark County have been upgraded. The remaining traffic signals in the Clark County system are expected to be upgraded in 2017 and 2018. Most of the work has been paid for using federal grants.
Clark County has been working to convert all of its coordinated traffic signal corridors to function within a central traffic responsive operation. Most cities and counties time their coordinated signals based on a fixed time of day approach, with the same timing plan used at the same time every day of the week.
In contrast, Clark County’s traffic signals communicate with a central server application that monitors actual volumes and congestion on the roads and selects the appropriate timing plan, based on the traffic conditions during the previous 10 to 15 minutes.
Clark County also has been working to install advanced systems to log performance data for traffic signals and arterial corridors. This equipment tracks numerous metrics, such as overall travel time and percentage of traffic arriving at the intersection with a green signal. Traffic engineers can make modifications to signal operations and monitor the effect on corridor speeds and other factors.
Clark County will begin installing adaptive signal technology on several corridors in late 2017 to help improve the flow of traffic. Three corridors will get adaptive signals:
- Northwest/Northeast 78th Street, from Northwest Ninth Avenue to Padden Parkway at Northeast 55th Avenue.
- Northeast Highway 99, from Northeast 63rd Street to Northeast 96th Way.
- Northwest/Northeast 139th Street, from Northwest Second Avenue to Northeast 20th Avenue.
These corridors already have traffic responsive operation, but the responsive system lags behind changes in traffic volumes by about 15 minutes. Traffic responsive operation also cannot be configured to shift operation based on specific incidents. Adaptive signals are able to change the signal operation on the corridors cycle by cycle and respond to incidents.
An example of how adaptive signal operation should better handle signal timing in the corridor is on Northeast 78th Street, from Northeast Hazel Dell Avenue to Northeast Highway 99. The signals on this portion of the 78th Street corridor are timed to reduce the potential for traffic to back up onto the northbound freeway off-ramp. The tight spacing of the freeway signal and the Northeast Highway 99 signal on Northeast 78th Street can cause backups.
The signals are timed to try to find the best way to clear the eastbound approach for Northeast 78th Street at Northeast Highway 99, thereby reducing the potential for traffic to back up onto the freeway off-ramp. Adaptive signals can be programmed to detect traffic backing up on the freeway off-ramp. The signal system will change to flush that traffic away from the ramps. Once the ramps are clear, the signal system will revert to a smooth flow operation to better serve all traffic.
The county also is developing standards for automated performance measures. Each corridor is being evaluated to determine the appropriate performance measure for each group of intersections in the corridor. These performance measures will help traffic engineers determine when corridors should be retimed, along with when a corridor is operating in a manner that needs immediate attention.
In late 2017, Clark County will begin providing real time video to the public from our pan-tilt-zoom cameras at intersections, along with live traffic congestion information.
Flashing yellow arrows
A new type of signal is being installed and retrofitted to county traffic signals
Flashing yellow arrows allow drivers to 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 (360) 397-2446 or submit an online road maintenance request.