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Tunnels Trimet West Side Corridor Light Rail
 

Lighting boosts security,
trims budget for train tunnels

The light rail tunnel lighting system may not seem that important to train passengers until the train suddenly shuts down. Then, passengers must have enough light to exit the tunnel safely.

Twin tunnels are part of the light rail system that transports passengers from downtown Portland, Oregon to outlying areas such as Beaverton and Hillsboro. As part of the Trimet West Side Corridor Light Rail Extension Project, the four-mile tunnels were originally designed with step lighting—the same type of lighting found in most automobile tunnels.

However, when the tunnel boring process required more of the budget than planned, cuts had to be made. The lighting designer had to recommend a less expensive lighting system that would still ensure passenger safety.

Elcon Associates, Inc. designed the tunnel lighting system. Rod Roche, the electrical project manager who was with Elcon at that time, indicated the lighting had to meet NFPA 101 Life Safety Code and NFPA 130, the code for fixed guideway systems. These codes require a minimum of 1-footcandle to illuminate the path of egress.

The West Side Corridor Light Rail tunnel operational considerations required that the trains must be able to run in either direction. Therefore, the illumination from the lighting system must accommodate train operator glare considerations from both directions.

Holophane Tunnel Predator® luminaires with 70-watt high-pressure sodium lamps were selected for the project and installed 10 feet above the top of the track rails and seven feet above the three-foot wide walkway along one wall. Because of the curve of the tunnel wall, the fixtures had to be mounted at a relatively low height. A 750-volt DC line running along the top of the tunnel also limited the area where the fixtures could be placed.

The Predator luminaires are mounted so they provide cutoff lighting, which guarantees there in no glare in the train operators’ eyes—no matter which direction the train is travelling.

Fixtures are spaced at 60 feet, with the system designed to prevent the “flicker effect,” a condition common to some tunnels. The “flicker effect” is an annoying sensation caused by the stroboscopic effect of passengers viewing closely spaced lighting sources.

The Predator units’ reflector system allowed the designer to increase the distance between the luminaires. Light level requirements were met with fewer fixtures, which, in turn, reduced the cost of the project. The light levels exceed the 1-footcandle requirement mandated by the NFPA codes.

Even though the trains shut down at night, the tunnels are illuminated 24 hours a day, seven days a week. Because the fixtures must provide illumination during an emergency situation, the units will not tolerate any bump in the power. The luminaires are backed up by a substantial uninterrupted power source that will keep the voltage constant until the diesel generator comes on line.

Because power panels could not be installed along the tracks, the Predator luminaires are powered at ground level at the Washington Park Station, the only station within the tunnel section of the line. The vertical distance from the power panels to the track level is more than 300 feet, which required extensive voltage drop calculations to ensure a robust, yet economical lighting power distribution system.

The lighting fixtures are mounted with a standard bracket attached with concrete anchors to the tunnel wall. The design was intended to accommodate the use of a truck-mounted high pressure washing system for periodic cleaning.

The Predator fixtures have proven very reliable and have functioned as intended. The illumination provided is more than adequate to meet and exceed the code mandated for emergency lighting in the tunnels.



 

 
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