The Robertson Tunnel is a twin-bore light rail tunnel through the Tualatin Mountains west of Portland, Oregon, United States, used by the MAXBlue and Red Lines. The tunnel is long and consists of twin tunnels. There is one station within the tunnel at Washington Park, which at deep is the deepest subway station in the United States and the fifth-deepest in the world. Trains are in the tunnel for about 5 minutes, which includes a stop at the Washington Park station. The tunnel has won several worldwide engineering and environmental awards. It was placed into service September 12, 1998. The tunnels pass through basalt layers up to 16 million years old. Due to variations in the rock composition, the tunnel curves mildly side to side and up and down to follow the best rock construction conditions. The tunnels vary from 80 to 300 feet below the surface. A core sample taken during construction is on display with a timeline of local geologic history. The east tunnel entrance is near Vista Bridge at the edge of the Goose Hollow neighborhood at the foot of Washington Park. The west entrance is along U.S. Highway 26 just west of the Finley-Sunset Hills cemetery, about a mile east of the junction with Oregon Highway 217.
Name
The tunnel is named for William D. Robertson, who served on the TriMet board of directors and was its president at the time of his death.
History
Several alternative alignments through the West Hills were studied, including an all-surface option along the Sunset Highway, an option with a half-mile-long "short tunnel", and an option with a three-mile "long tunnel". TriMet selected the "long tunnel" in April 1991. Construction began in the summer of 1993 at the west end, employing the conventional mining technique of drilling and blasting due to the loose mixture of materials. More than 75 tons of explosives were used and mining progressed about a mile into the hill. East end construction began in August 1994 with a customized tunnel boring machine. About a thousand workers from 230 construction firms were involved in the 18-mile westside MAX line, including those who built the tunnel and installed the reinforced concrete liner, tracks and wiring. One worker was killed while operating equipment. Tunnel construction continued 24 hours a day, six days per week. The north tunnelers met after 16 months on December 29, 1995, and the boring machine began the south tunnel in April 1996. Work in the south tunnel took only four months before the tunneling teams met on August 15, 1996. To complete the west end at the cemetery, 14 bodies were relocated. The original estimate for the tunnel was $103.7 million, but the final price tag came to $184 million, largely due to challenges posed by unexpected loose layers of silt and gravel, and crumbling basalt which prevented the boring machine from working effectively.
Route
The tunnel generally follows – but remains north of – U.S. Highway 26, diverging the most in the Oregon Zoo area. The elevation at the west end is higher than the east but there is very little perceptible slope except for several gentle, short grades which exist presumably to follow the easiest-to-bore rock stratum. During construction, the east portal was west of Canyon Road, below City of Portland Reservoir 4. After completion, the road was raised and an overpass placed over the track. This effectively extended the original bored-and-blasted tunnel east by about, making the final length, so that it would emerge to the east of Canyon Road, and on the south side of Jefferson Street. Beginning at the east end, under Canyon Road the tunnel turns SSW for about where it turns WSW under the large field east of the Elephant House. Twelve hundred meters later it is directly under and follows SW Kingston Road at a point north of the zoo's elephant exhibit. For the next, it arcs until almost directly westward and straightens for to arrive at Washington Park. After the station, it passes under the south side of the World Forestry Center's main building and turns 4° northward and continues for its longest straight stretch of. At the point it passes under SW Skyline Road north of the Sylvan Bridge, it turns slightly southward, it turns right in a long gradual arc exactly paralleling Sunset Hwy. The arc continues at the same rate after the west portals, and is due west about past the portals.
