Major bridges require thousands of lights working together in a unified and automated way to keep drivers safe and traffic running efficiently.
The new SR 520 Bridge -- stretching across Lake Washington between Seattle, WA and East side communities like Redmond and Bellevue -- will soon hold the title of the world's longest floating bridge, spanning 7,710 feet. Scheduled to open in 2017, the $4.25 billion project will replace the 7,500 foot Evergreen Point bridge built on the same site in 1963 that has come under disrepair. It will accommodate twice the vehicle traffic as the old bridge, and support pedestrian traffic with a 14 foot wide bike and walking path. Made up of 77 floating pontoons anchored by underwater weights, the new SR 520 is engineered like a temporary bridge or military crossing. Building a standard suspension bridge across it was not a viable option because Lake Washington can be more than 200 feet deep over a soft mud bottom.
More than 7,000 lights illuminate the bridge. Fluorescents light the roadway, and metal-halide lighting keep the 10-foot pathways for pedestrians and cyclists safe at night. Iconic "sentinels" on each end of the bridge use LEDs to change the color and style of lighting, while translucent spires atop each sentinel house additional lights, illuminating the structures from the inside. Compared to the original bridge's design, this lighting scheme delivers far higher luminous efficiency, more adjustability, and greater control.
Lighting on the two miles of interconnecting bridge roadway -- including inside the three tunnels on the East side of Lake Washington which are in use 24 hours a day -- is controlled using ELMS software from Gridaptive Technologies. The complete end-to-end ELMS (Electrical Lighting & Management System) was designed, installed and commissioned by PLC Multipoint, a lighting manufacturer and system integrator located in Everett, WA. ELMS provides the ability to easily configure, control and monitor roadway and tunnel lighting circuits using public data communication infrastructure from Washington State's DOT offices 15 miles away in Shoreline, WA. Three tunnel lighting control cabinets contain a datalogger/controller that sends real-time performance data including current, voltage, and power usage to the Shoreline based server and workstations via fiber optic communications. Engineers monitor and set operational attributes such as extinguishing or dimming lights for half of the night. Performance parameters applied to these fixtures can be automatically overridden and commanded to full brightness from a traffic count sensor.
As Gridaptive and its partner PLC Multipoint developed the ELMS for SR 520, the companies quickly realized that they would need highly reliable, fully redundant embedded computers to connect all critical lighting equipment to a central control location.
"Our goal was to design an ELMS NTCIP 1213 compliant system to assure the right amount of light when drivers needs it, depending on factors obtained through monitoring equipment such as vehicle flow detection, vehicle speed and brightness levels based on weather, season, and time. In addition to great safety, this approach stretches the luminaires overall lifetime and greatly reduces daily energy cost, says Jim Frazer of Gridaptive. "We didn't want take any risks of failures when drivers' lives are at stake. It was critical for the platform to be easy to develop for, and the manufacturer to be easy to work with. That's why we chose Moxa."
Moxa specializes in extremely reliable networking and communications hardware and provided Gridaptive with rugged embedded computers to dynamically adjust the luminance in real time to be safe, comfortable, efficient, and economical. Illumination of all segments of the bridge and in the tunnels is regulated constantly through sensors. Light level transitions are controlled so that they are within the eye adaption rate of the drivers, eliminating over or under lighted conditions, so as to ensure the safety of drivers.
According to Gridaptive's Jim Frazer, the ELMS seamlessly interfaces with the Moxa computers to give operators easy navigation for monitoring lighting system status as well as for providing operational control either locally or via a SCADA network. The Moxa units also exhibited exceptional reliability, thanks to 100% burn-in and wide temperature testing, as well as features such as KV isolation protection and dual LAN ports for network redundancy
"With the built-in VGA output interface, the computers are suitable for use with SCADA systems, and they have the durable design necessary for bridge conditions subject to ice, rain, waves, snow and high winds," Frazer notes.
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