Lighting Mountains

Oct. 1, 2005

The coast and Cascade Mountain ranges run through the state of Oregon, dividing it into three separate regions. Highways that link the regions rely on tunnels to go under the mountains, and the tunnels rely on their lighting systems to improve vehicular safety.

The coast and Cascade Mountain ranges run through the state of Oregon, dividing it into three separate regions. Highways that link the regions rely on tunnels to go under the mountains, and the tunnels rely on their lighting systems to improve vehicular safety.

Just under a dozen of Oregon’s mountain tunnels were constructed between 1930 and 1970. Lighting systems in the older tunnels were upgraded in the 1960s, but little had been done to upgrade them since that time. By 1990, the lighting wiring systems were failing and replacement parts were impossible to obtain. As maintenance costs skyrocketed, the Oregon Department of Transportation initiated a program to renovate the lighting systems in the tunnels. The goals of the program were to replace failing equipment and improve safety and light levels. The renovated tunnels are located in various parts of the state, each with unique challenges. For example, the Vista Ridge and Jefferson Street tunnels are in an urban environment with high volumes of traffic. Arch Cape and Cape Creek tunnels are near the coast and must contend with corrosive, salt-laden fog. Tooth Rock and Salt Creek tunnels are subject to ice storms and snow that can accumulate up to 5 ft high. The condition of interior finishes varies considerably, from reflective tile to concrete to raw rock. The Petersen and Elk Creek tunnels form critical links between the coast and the interior with no easy bypass.

Hitting the threshold

During daylight hours, the goal of every tunnel lighting system is to reduce the black-hole effect for vehicles entering the tunnel. Effective tunnel lighting improves safety and gives drivers confidence that they can see inside a tunnel as they approach it, making them more likely to maintain speed and sustain traffic flow. Overcoming the black-hole effect requires providing a high level of light immediately inside the tunnel in an area known as the threshold zone. The design challenge is to determine a level of light for the threshold zone that permits safe travel but doesn’t have excessive amounts of light (along with the associated costs of installation, maintenance and energy).

The threshold zone light level is typically determined by assessing the luminance of the sky and surfaces surrounding the tunnel portal. Reflectance of sunlight from the portal and roadway construction materials, adjacent natural and man-made features and surrounding vegetation all contribute to the luminance level. In its “Recommended Practice for Tunnel Lighting,” the Illuminating Engineering Society (IES) publishes a table of recommendations for threshold light levels based on typical portal and sky arrangements. In Oregon, the mountains run north to south and the tunnels run east to west. East-to-west tunnels are challenging because the sky is very bright at sunset and sunrise. Accordingly, the IES recommends high threshold zone light levels for these tunnels.

The IES also permits the use of a calculation, called the Lseq method, to determine threshold zone levels. This calculation is particularly helpful for existing tunnels where the portal luminances can be measured. The luminances must be measured under a variety of daytime conditions. The most stringent are with the morning or afternoon sun directly in line with the portal.

For the Oregon tunnels, the Lseq field measurements and calculations revealed that light levels lower than the IES table of threshold zone levels could be used. The results of the Lseq calculations were combined with a review of the tunnel’s accident history under the previous light level to determine an appropriate new threshold zone light level. In all cases, the new illumination design level exceeded the previous level.

Field measurements of the Vista Ridge Tunnel showed that white paint on the outside of the concrete portal significantly increased the light level required on the threshold zone. The white paint was sandblasted off and replaced with a darker tan, helping to minimize the amount of light required in the threshold zone. In long tunnels, the interior light level is gradually reduced after the threshold zone, allowing the driver’s eye to gradually adjust from high to low light levels. Every tunnel but Vista Ridge and Tooth Rock are two-way tunnels in a single tube. In these two-way tunnels, the threshold zone lighting of one lane also provides the lower light level required in the opposite lane.

While not as critical as road luminance, the luminance of the walls contributes to the perception of light in a tunnel. The walls form a significant part of the motorist’s visual field and serve as a backdrop to help them see pedestrians and bicyclists who may be in the tunnel. Uniform illumination of the walls presents a comfortable visual image.

Many of the Oregon tunnel lighting renovations were coupled with refinishing of the interior walls. The Arch Cape Tunnel has a bare rock interior finish. This coastal tunnel has significant bicycle usage, and safety was a critical concern. The addition of a white-painted curb barrier and panel effectively enhances the motorists’ ability to see bicyclists.

Having enough light

Lighting control technology is moving forward, and in general the industry is following suit. Tunnel threshold zone light levels are determined by full sunlight conditions; however, threshold zone light levels can be reduced on cloudy days to save energy.

Oregon is adjacent to the Pacific Ocean and has many overcast days. Programmable lighting controls were installed on the Vista Ridge Tunnel project but were later removed in favor of tried-and-true photocells and relays. If a photocell or relay fails, it is easy to unplug and replace it.

Programmable systems require reading the manual or previous training, and the electrician may not have that experience. After the Vista Ridge Tunnel was completed, the tunnel renovation officials opted for simple, noncomputer-based systems. Many of the power supplies and controls are in exterior cabinets without environmental controls. Traditional photocells and relays also stand up very well to harsh environments, while computer-based systems tend to be more sensitive. Most of the tunnels utilize three of four levels of controls: a nighttime level, a full daytime level and one or two intermediate daytime levels. For further simplification, the night lighting for most of the tunnels was placed on separate circuits and left to run continuously.

Sodium intake

During the 1960s, mercury-vapor and fluorescent light fixtures were used to illuminate tunnels, with the latter being the choice for most of the tunnels in Oregon. Fluorescent tubes are long and fluorescent fixtures require lengthy gaskets. Water, insects and dirt tend to penetrate gaskets and compromise the performance of the light fixture. Light fixtures with short gaskets will stand up better than those with long gaskets. Storing, handling and installing fluorescent lamps that range from 4 to 8 ft can be cumbersome.

Another consideration is safety for maintenance workers. Tunnels are very tough places to work. Work is often done from a bucket truck in the evening under adverse weather conditions, with traffic oblivious to the safety of the maintenance crew. All systems were designed to minimize the amount of time maintenance personnel spend in the tunnel.

Oregon Department of Transportation personnel reviewed samples of different fixture types before choosing high-pressure sodium lamps in modular fixtures that are specifically designed for tunnel environments. Modular fixture construction permits electricians to easily isolate and replace one part of the fixture if it fails. Plug-in/plug-out construction eliminates the need to do wire splicing in the tunnel. The modular features include an easily removable lens and ballast. When compared with older fluorescent fixtures, the high-pressure sodium source uses less energy and the light is more effectively directed. The fluorescent fixtures were not as effective because they sent light in all directions, including the ceiling where it is not needed.

In all of the tunnels, the light levels were increased more than 50% without increasing the size of the service or energy consumption. Wiring is generally placed in corrosion-resistant 304L stainless-steel wireways and galvanized steel raceways.

Parts of history

Many of the Oregon tunnels are over 35 years old and have historical significance, with a need to preserve their appearance. Of particular concern were the Salt Creek and Tooth Rock tunnels, which were constructed during Franklin D. Roosevelt’s work programs of the 1930s. Their portals show a masonry craftsmanship not often found on today’s highways.

Preserving the historical appearance of these tunnels meant not running shiny new conduit across the portal face and into the tunnel. This presented a design challenge, because many of the power supplies were located in front of the associated tunnel with no easy way to get conduits inside to the light fixtures. For most of the tunnels, this problem was solved by core drilling through the neck of the tunnel liner in an area between the portal and the bore.

The wiring in the Vista Ridge Tunnel was placed in an unused ventilation shaft that is completely out of site.

The tunnel power supplies were located as unobtrusively as possible, and painted to match the surrounding environment. Typical locations are inside of adjacent structures, along a neighboring bicycle path or under an approaching viaduct. The benefits of improving the tunnel illumination systems are clear: maintenance costs are down, light levels are up and energy efficiency is improved. The higher illumination levels improve safety and enhance the flow of traffic. Careful design and selection of system components have given the state of Oregon a lighting system with exceptional performance and value.

About The Author: Degnan, P.E., is a member of the ANSI/IES Roadway Lighting Committee and principal of a design studio at Sparling, an electrical engineering and technology consulting firm with offices in Seattle and Portland.

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