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Tunnels McCarran Tunnel, Las Vegas
 

Lighting promotes safety,
energy savings for McCarran Tunnel



Drivers entering a dark tunnel from bright sunlight may not be able to see traffic hazards that exist in front of them. This is why good lighting at the entrance of a roadway tunnel is important.

It was even more crucial for the new 2,740-foot, six-lane vehicle tunnel at McCarran Airport in Las Vegas, where external brightness in the summertime may be as high as 10,000 footcandles.

"We were particularly concerned about the tunnel entrance and how to avoid the 'black hole' effect that motorists experience when traveling from a very bright external light level to a comparably darker level," explained Ernie Gomes, Electrical Layout Supervisor, Bechtel Corporation, San Francisco, engineers and designers for the project.

Energy costs were a consideration, which is why high pressure sodium luminaires, with their high lumen to watt ratio, and high coefficient of utilization, were selected.

"In designing the lighting system, we needed to determine the lamp wattage and luminaire spacing that satisfied the tunnel entrance lighting level requirements and the proportional steps for reducing the light level within the tunnel. At the same time, through the use of switching, we wanted to be able to use the same luminaire spacing and lamp wattage to achieve nighttime and intermediate lighting levels," Gomes said.

Luminaires installed are Holophane ProBeam®, tunnel luminaires with 400 watt, 250 watt, 150 watt and 100 watt lamps.
Holophane's Computer Aided Lighting Analysis (CALA) software was employed to quickly analyze different layouts and configurations, and to fine-tune the final design.

During the design process, the decision was made to use three levels of light, instead of two, to reduce energy costs. The lighting system includes a daytime level, nighttime level, and an energy-saving intermediate level for use during twilight or overcast periods when the outdoor ambient light level is not full brightness.

A sunshade was installed at the tunnel entrance to lower the outdoor brightness to approximately 1,000 footcandles, versus 10,000 footcandles without the sunshade. The reduction in external ambient light resulted in a corresponding lower light level requirement in the threshold zone.

Mounting height for all luminaires is 18 feet. The longitudinal spacing of the fixtures varies from eight feet at the tunnel entrance (threshold zone), to 24 feet in the transition zones, and 48 feet in the interior zone.

Luminaires are aimed away from the direction of oncoming traffic, which totally eliminates glare to the driver and the "flicker effect" inherent in other tunnel lighting systems. Average design footcandle levels range from 130 footcandles at the tunnel entrance, to 33 and 13 in the transition zones, 6 in the interior zone, and 3 throughout the tunnel at night.
"One of the comments we have heard most often is that there is no glare when entering and driving through the tunnel since the lamps are not visible to the motorist," Gomes said. "The walls and other vehicles are very well lighted. Since these are the things a driver looks at in a tunnel, safety is improved and the motorist feels comfortable."

A sunshade was installed at the tunnel entrance to lower the outdoor brightness to approximately 1,000 footcandles, versus 10,000 footcandles without the sunshade. The reduction in external ambient light resulted in a corresponding lower light level requirement in the threshold zone.

The Holophane luminaires meet stringent hose down requirements for tunnel wash down. The design basis for the tunnel included provisions for regular relamping of the fixtures at approximately 80 percent of rated lamp life, with regular cleaning of the tunnel walls and luminaires.

Tunnel lighting is energized 24 hours a day, using three different lighting levels determined by the amount of external ambient light. The different levels are switched on and off by photo cell, and are also controlled by the airport computer system.

Although not related to the lighting system, the tunnel has an extensive ventilation system, along with a traffic surveillance and control system which includes CCTV, changeable message signs, a fire monitoring system, communication system, radio rebroadcast system, and UPS system.

The tunnel is owned by Clark County Department of Aviation.



 

 
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