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Getting better performance out of our traffic signals is a high priority, for the Clark County Council and Public Works.
Technology
For decades, most traffic signals were governed by a programed 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, rather than a collection of individual intersections.
Clark County has been working to convert all of its coordinated traffic signal corridors to function within a central traffic-responsive or adaptive 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.
Learn more about the county's traffic signal optimization program by watching this February 2012 CVTV video .
Video Link: https://www.youtube.com/watch?v=4S9eAYXj1uw
Clark County began installing adaptive signal technology on several corridors in late 2017 to help improve the flow of traffic. Three corridors got 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 programed 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.
Upcoming work
The county 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 re-timed, along with when a corridor is operating in a manner that needs immediate attention.
Battery backup systems
Clark County has installed battery backups at every signalized intersection.
Battery backups keep county traffic signals operating through power failures lasting as long as 6 hours. Most power outages in the region are less than 40 minutes.
During some windstorms, electrical power will go on and off up to 15 times in an hour. Providing continuous power to traffic signals improves safety for drivers, pedestrians and cyclists.
Battery backup systems also buffer the power coming into the traffic signal to protect sensitive electronics.
If you do come across a signalized intersection that has gone “dark” because of a power failure, you should treat the intersection as a four-way stop.
For more information, watch this September 2012 CVTV video:
[video: https://www.youtube.com/watch?v=YJlPZUy5lp4]
Flashing yellow arrows
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.
Radar detection systems
Clark County is working to get vehicle detection systems out of the pavement. The county has installed radar stop bar detection and radar advance detection at most of the signals.
The radar stop bar detection system is designed to detect all vehicles, including bicycles and motorcycles. The radar advance detection system monitors all approaching vehicles for their current speed and location, calculating an estimated time of arrival to the stop bar.
The radar advance detection system will extend the green signal, when possible, to accommodate a driver who is in a “can’t stop/can’t go” decision point based on the driver’s location and speed. This system is designed to reduce the potential for a driver needing to perform a panic stop, thereby improving safety.
LED luminaires
Clark County has upgraded all county-owned street lighting to LED luminaires. The county started converting the older, salmon-colored high-pressure sodium lights to LED luminaires in 2012.
LED luminaires use about half the power of the older generation of street lights and last much longer. High-pressure sodium lights tend to last 1 to 2 years while LED lights are expected to last at least 10 years.
Lower power costs and reduced maintenance costs mean that the initial expense to install LED luminaires is typically paid off in 6 to 7 years.
LED vehicle/pedestrian signal indicators
In 2014, Clark County upgraded almost all of its vehicle signal indicators to use LEDs, which improved visibility, reduced power consumption and lowered maintenance costs since older incandescent bulbs would burn out within a year of being installed.
New LED signal bulbs have a much longer life, typically more than 10 years. LED bulbs use about 10 percent of the power that older incandescent lights used. Improved reliability and reduced power usage means that the LED signal indicators pay off the investment within 4 years of installation.
Accessible pedestrian push buttons
Clark County is upgrading all of its pedestrian push buttons to comply with Americans with Disabilities Act requirements for enhanced pedestrian push buttons. The buttons provide locater tones to help blind and sight-impaired pedestrians locate the buttons, along with wayfinding sounds to help them cross the street.
All of the county intersections with traffic signals have new accessible pedestrian push button systems.
The county also is adding verbal messages to buttons to provide enhanced information for pedestrians who are blind or sight impaired.
Countdown pedestrian indications
In 2014, Clark County finished upgrading all of its pedestrian crossings at signalized intersections to include countdown timers. This allows pedestrians to know how much time they have left to cross the road.
Report signal concern
If you see a malfunctioning traffic signal, please call 564.397.2446 or submit an online road maintenance request.