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Tunnels Wilcox Tunnel; Chattanooga, TN

Predator luminaires boost visibility
in narrow Chattanooga tunnel

Cutting through Missionary Ridge, the two-lane Wilcox Tunnel in Chattanooga, Tennessee, is older and was previously lighted with 150-watt high pressure sodium luminaires.

According to W. L. Rice, senior engineer, Engineering Division, Chattanooga Electric Power Board, lighting not only had less footcandles, but the fixtures were hard to clean.

"Because Wilcox Tunnel is located in an industrial area, there is a lot of truck traffic," Rice explained. "The tunnel, which is semi-circular, is also very narrow."

When a lighting retrofit was initiated by the city, one requirement was to install luminaires that could withstand the force of high pressure water so the tunnel could be steam cleaned. The units chosen are Holophane Predator luminaires with 400-watt high pressure sodium lamps.

A total of 92 fixtures are used in the 1300-foot long tunnel, with placement and spacing determined by Holophane's Computer Aided Lighting Analysis (CALA) software. Mounting height is 15'7" with spacing varying from 5' to 25'.

Luminaire numbers are more concentrated at the tunnel entrance, allowing drivers' eyes to adjust from the bright sunlight. Spacing becomes greater toward the center of the tunnel, with footcandle levels decreasing from 160 at the entrance to 48 halfway through. All of the fixtures are lighted during the day, with half of the units illuminated at night. The units are controlled by a sun switch.

"Since the Predator luminaires are typically used in one-way tunnels, one of our concerns was how to mount the units in a two-way tunnel to avoid driver glare and the 'zebra effect', or streams of hot and dark spots on the walls," said Rice. "The luminaires are designed with a junction box mount to give a 15 degree tilt from the mounting plane. Mounted at 90 degrees, they provide a highly visible and comfortable environment."

Tunnel fixtures will be maintained by the Electric Power Board.


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