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Tunnels Lehigh Tunnel, Pennsylvania

Lehigh tunnel "lights up" with Holophane luminaires

Travelers on the Pennsylvania Turnpike can literally see light at the end of the new Lehigh Tunnel. The tunnel threshold and transition zones are illuminated with 1,000+ Holophane Lighting Module 600 high pressure sodium luminaires with more than 500 installed on each end.

Lighted according to IES standard RP-22, the tunnel includes 1000 feet of threshold and transitional zones at each end to help drivers' vision adjust to the dramatic change in light levels upon entering and leaving the tunnel.

According to Ken Slippey, design liaison engineer for the Pennsylvania Turnpike Commission, the gradation in lighting within the tunnel is a new feature the Turnpike Commission is considering for other tunnels.

Entering and exiting the tunnel, the threshold zone was designed for a minimum of 300 footcandles maintained. Progressive transitional zones are 100 footcandles, 70 footcandles, and 35 footcandles. The remainder of the tunnel maintains a 10 footcandle level using conventional fluorescent fixtures. These levels are according to IES standards and based on traffic flowing at a speed of 55 miles per hour.

Light levels within the tunnel are controlled by computer at a control center console. Frequent adjustments are made automatically according to the time of day or night and the ambient light levels outside the tunnel.

"It is critical that the change in illumination from the exterior of the tunnel to the interior not be too sudden or drastic so as to overcome the black hole effect," said Paul Doran and Jim Strempek, engineers for GSGSB, the application engineering firm that spearheaded the project.

"On a normal bright day, daytime illumination levels outdoors readily exceed 1,000 footcandles." Within the transitional lighting zones, the Holophane Lighting fixtures use 400 watt, 250 watt, and 150 watt lamps, with the higher wattage lamps being installed in those fixtures near the ends of the tunnel.

In the design of the lighting, the choice of the fixtures and especially the physical constraints within the tunnel were major considerations. The fixtures had to be positioned out of the path of traffic yet still achieve the proper illumination distribution for driver comfort and safety.

"The luminaires also had to be able to overcome the tunnel's very harsh environmental conditions," Slippey added. "Moisture is an inherent problem within a structure of this type, along with the exhaust emissions from the vehicles using the tunnel."

Doran indicated Holophane Lighting fixtures were specified for application on the Lehigh Tunnel project based on his experience with other tunnel and underpass applications in Arizona and Pennsylvania.

"The Module 600 fixtures passed the rigid spray tests dictated by the contract specifications," Strempek said. "The units include a protected starter that will sense any lamp malfunction and shut down high voltage pulses."

Special sealing compound and hinge design modifications were incorporated into the fixtures; additionally the luminaires were gasketed to prevent soot accumulation from diesel fumes. The Module 600 luminaires provide for a 10-year guarantee on parts.

Holophane Lighting's Computer Aided Lighting Analysis (CALA) software was used to determine lamp wattage and fixture placement to achieve the horizontal and vertical footcandles required. The HID fixtures are installed over opposing curbs in the first transition zone, with spacing increasing and lamp wattage decreasing as the design footcandle levels decrease .
"The response to the transitional lighting has been very favorable," Slippey said.

Maintenance of the lighting fixtures will be performed periodically by closing the entire tunnel tube and routing traffic through the older tunnel for short periods of time. A truck fitted with a high pressure hose will wash the luminaires, and the lamps will be changed as needed.

The new tube of the Lehigh Tunnel has eliminated the only two-lane section of the 110-mile Northeast Extension of the Pennsylvania Turnpike, which joins the Philadelphia area with the popular Pocono Mountains. In August 1989, the Turnpike Commission estimated that an average of 22,000 vehicles used the tunnel every day. On weekends, traffic volumes tended to increase, causing undesirable back ups .

The Lehigh Tunnel is the first automobile tunnel in the United States to use the New Austrian Tunneling Method (NATM) for construction. While the tunnel tube was blasted as with conventional tunnels, the interior is supported by a concrete fixture sprayed on the exposed rock surface, as opposed to the usual procedure of installing rigid steel supports.
The NATM method is purported to be faster and less costly. The price tag for constructing the new 4,380-foot Lehigh Tunnel was in excess of $.37 million.

Headquartered in Columbus, Ohio, Holophane Lighting, Inc. has been the leader in light control for more than 99 years. The company provides lighting systems for commercial, industrial, emergency, and outdoor applications.


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