Vista Ridge Tunnels
Encyclopedia
Tunnel
A tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...
s through the Tualatin Mountains
Tualatin Mountains
The Tualatin Mountains are a range of hills on the western border of Multnomah County, Oregon, United States...
("West Hills") of Portland, Oregon
Portland, Oregon
Portland is a city located in the Pacific Northwest, near the confluence of the Willamette and Columbia rivers in the U.S. state of Oregon. As of the 2010 Census, it had a population of 583,776, making it the 29th most populous city in the United States...
, USA through a hillside locally known as Vista Ridge which is a half mile (1 km) west of downtown Portland. Sunset Highway
Sunset Highway (Oregon)
The Sunset Highway No. 47 , in the state of Oregon, is an official designation for the portion of U.S. Route 26 between its western terminus, south of Seaside, and the interchange with Interstate 405 in downtown Portland...
, also known as U.S. Route 26, is carried through the tunnels, three lanes in each direction. The average daily combined traffic volume was 145,299 vehicles in 1999
and 139,300 in 2005.
They are the busiest tunnels in Oregon
and 12% busier than I-5's 6-lane Interstate Bridge
Interstate Bridge
The Interstate Bridge is a pair of nearly identical steel vertical-lift, through-truss bridges that carry Interstate 5 traffic over the Columbia River between Vancouver, Washington, and Portland, Oregon, in the United States...
and 2% busier than I-205's 8+ lane Glenn L. Jackson Memorial Bridge
Glenn L. Jackson Memorial Bridge
The Glenn L. Jackson Memorial Bridge, or I-205 bridge, is a segmental bridge that spans the Columbia River between Vancouver, Washington and Portland, Oregon....
.
The eastbound tunnel is 1001.0 feet (305 m) in length; the westbound tunnel is 949 feet (289 m). Both have 41 ft (12.5 m) of horizontal and 15.58 ft (4.75 m) of vertical clearance. The eastbound tunnel was completed in 1969, the westbound a year later.
There is a six-percent grade through the tunnels. Most of the tunnels' lengths are straight, though they curve southward at the west ends 35°.
The tunnels were built with ventilation shafts which were never used. Instead, the shafts were later adapted for electrical wiring, so as to improve tunnel illumination without marring the tunnels' appearance with visible conduit
Electrical conduit
An electrical conduit is an electrical piping system used for protection and routing of electrical wiring. Electrical conduit may be made of metal, plastic, fiber, or fired clay. Flexible conduit is available for special purposes....
.
To improve tunnel safety for motorists, and decrease the tunnel lighting requirements, the original tunnel entrance faces were sandblasted to remove white paint and repainted a less luminescent
Luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...
tan color to reduce the range of visual light adaptation required by drivers. At one time there were computer-based electronic light controls, but they were replaced by relatively simple photo detectors and relay
Relay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...
s for durability and simplicity. The night lighting level is enabled permanently and is supplemented by two or three levels of daytime lighting.
Except directly over the tunnels, the hillsides are steep and undeveloped forest, with some residential development along the top of the ridges. Landslides occasionally occur, but are usually minor and quickly cleared.
The tunnels have been closed to hazardous material transport since November 1, 1994.
As a result, US 26 is closed to hazardous material transport between I-405
Interstate 405 (Oregon)
Interstate 405 is a short Interstate Highway in Portland, Oregon. It forms a loop from Interstate 5 that travels through downtown Portland west of the Willamette River.-Route description:...
and Oregon Route 217.
The tunnels are located nearly at the bottom of a hill where the road gradient averages 6.5% over 2.25 mi (3.6 km). Close to the east portals is a 130 foot (40 m) tunnel underpass carrying SW 18th Avenue. Just outside the west portals is a 650 foot (200 m) tunnel under the lanes which carries eastbound Canyon Road
Canyon Road
Canyon Road is a road connecting Beaverton and Portland, Oregon, United States. It was the first road between the Tualatin Valley and Portland and contributed significantly to Portland becoming the area's major deep water port, and subsequent early growth of the city.The total modern length is...
from the exit ramp into Goose Hollow
Goose Hollow, Portland, Oregon
Goose Hollow is a neighborhood in southwest Portland, Oregon. It acquired its distinctive name through early residents’ practice of letting their geese run free near the wooded ravine in the Tualatin Mountains now known as the Tanner Creek Canyon and in the now infilled Tanner Creek Gulch...
. The Robertson Tunnel
Robertson Tunnel
The Robertson Tunnel is a tunnel through the west hills of Portland, Oregon, U.S. for the TriMet public transit MAX Light Rail system. The tunnel is 3.1 miles long and consists of twin 21 foot diameter tunnels. There is one station within the tunnel at Washington Park, the third deepest such...
for MAX Light Rail is underground approximately 800 feet (250 m) to the west.