Vista Ridge Tunnels

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The east end of the Vista Ridge Tunnels face downtown Portland and are under a residential neighborhood.
The east end of the Vista Ridge Tunnels face downtown Portland and are under a residential neighborhood.
View at mid-tunnel eastbound. Both tunnels curve noticeably, requiring streetlights even on this sunny afternoon with the sun shining in the west end of the tunnel.
View at mid-tunnel eastbound. Both tunnels curve noticeably, requiring streetlights even on this sunny afternoon with the sun shining in the west end of the tunnel.
The west end of the Vista Ridge Tunnels
The west end of the Vista Ridge Tunnels

The Vista Ridge Tunnels are highway tunnels through the Tualatin Mountains ("West Hills") of Portland, Oregon, USA through a hillside locally known as Vista Ridge which is a half mile (1 km) west of downtown Portland. Sunset Highway, 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[1] and 139,300 in 2005.[2] They are the busiest tunnels in Oregon[3] and 12% busier than I-5's 6-lane Interstate Bridge and 2% busier than I-205's 8+ lane Glenn L. Jackson Memorial Bridge.[4]

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 finished a year later.[5][6]

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°.[7]

The tunnels were built with ventilation shafts which were never used. Instead, the shafts were later adapted for electrical wiring to improve tunnel illumination but without marring the tunnel's appearance with visible conduit.[8]

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 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 relays for durability and simplicity. The night lighting level is enabled permanently and is supplemented by two or three levels of daytime lighting.[8]

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.[9]

The tunnels have been closed to hazardous material transport since November 1, 1994.[10] As a result, US 26 is closed to hazardous material transport between I-405 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[11] from the exit ramp into Goose Hollow. The Robertson Tunnel for MAX Light Rail is underground approximately 800 feet (250 m) to the west.

[edit] See also

[edit] References

  1. ^ Oregon Transportation Institute (November 5, 1999). Analysis of the Westside Corridor Travel Study—Did Westside Light Rail Really Reduce Traffic Volumes?. Retrieved on 2007-08-04.
  2. ^ Oregon Department of Transportation (2006-09-20). 2005 Traffic Volumes on State Highways 60 (84 on page). Retrieved on 2007-08-25.
  3. ^ Oregon Department of Transportation—Bridge Engineering Section (April 2007). 2008-2011 Draft Statewide Transportation Improvement Program—Evaluation of the State Bridge Program 26 (25 on page). Retrieved on 2007-08-25.
  4. ^ Glenn L. Jackson Memorial Bridge carries 137,000 average daily traffic; the Interstate Bridge, 124,500. Obtained 2004 values from Average Daily Traffic on Oregon’s Interstate Highways 1954–2004 (PDF) 2, 4. Oregon Department of Transportation (May 10, 2006). Retrieved on 2007-08-29.
  5. ^ Vista Ridge Tunnel (#9103+047+07353). Historic Bridges of the United States. Retrieved on 2007-07-30.
  6. ^ Updated August 1999 by Rosalind Keeney, ODOT Cultural Resource Specialist; Revised September 2002 by Robert W. Hadlow, Ph.D., ODOT Historian (September 2002). Appendix A: Highway Tunnels of Oregon (PDF). Oregon Department of Transportation. Retrieved on 2007-08-04.
  7. ^ Determined by rotating satellite image with photoshop.
  8. ^ a b Jim Degnan, P.E. (October 2005). Tunnel Lighting. Roads and Bridges. Sparling electrical engineering and technology consulting. Retrieved on 2007-08-04.
  9. ^ News Release: Landslide Repair Work Closes Westbound U.S. 26. Oregon Department of Transportation (April 13, 2007). Retrieved on 2007-08-04.
  10. ^ Transportation of Hazardous Materials; Designated, Preferred, and Restricted Routes. Federal Register: December 4, 2000 (Volume 65, Number 233) 75771-75816. U.S. Department of Transportation, Federal Motor Carrier Safety Administration (December 4, 2000). Retrieved on 2007-07-30.
  11. ^ Before the Sunset Highway was built, the two lane Canyon Road extended into Goose Hollow. Street signs near the Vista Bridge indicate the junction of SW Jefferson Street and SW Canyon Road.

[edit] External links