The tunnel generally follows – but remains north of – U.S. Highway 26, diverging the most (¹⁄₃ mile (540 meters)) 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 430 feet (130 m), making the final length 2.93 miles (4.71 km), so that it would emerge to the east of Canyon Road, and on the south side of Jefferson Street (immediately east of where Canyon Road bends from north to east and becomes Jefferson Street).

Beginning at the east end (traveling westward), under Canyon Road the tunnel turns SSW (202°) for about 300 m (980 ft) where it turns WSW (236°) under the large field east of the Elephant House.
Twelve hundred meters (4000 ft) later it is directly under and follows SW Kingston Road at a point 250 m (820 ft) north of the zoo's elephant exhibit.
 For the next 250 m (820 ft), it arcs until almost directly westward (263°) and straightens for 300 m (980 ft) 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 (267°) and continues for its longest straight stretch of 900 meters (3,000 ft).
 At the point it passes under SW Skyline Road 150 meters (490 ft) north of the Sylvan Bridge, it turns slightly southward (253°) and—300 m (980 ft) later—goes under the Finley-Sunset Hills building and water feature.
 For the remaining 500 m (1,600 ft)), 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 (270°) about 500 m (1,600 ft) past the portals.
The tunnel generally follows – but remains north of – U.S. Highway 26, diverging the most (¹⁄₃ mile (540 meters)) 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 430 feet (130 m), making the final length 2.93 miles (4.71 km), so that it would emerge to the east of Canyon Road, and on the south side of Jefferson Street (immediately east of where Canyon Road bends from north to east and becomes Jefferson Street).
Beginning at the east end (traveling westward), under Canyon Road the tunnel turns SSW (202°) for about 300 m (980 ft) where it turns WSW (236°) under the large field east of the Elephant House. Twelve hundred meters (4000 ft) later it is directly under and follows SW Kingston Road at a point 250 m (820 ft) north of the zoo's elephant exhibit.  For the next 250 m (820 ft), it arcs until almost directly westward (263°) and straightens for 300 m (980 ft) 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 (267°) and continues for its longest straight stretch of 900 meters (3,000 ft).  At the point it passes under SW Skyline Road 150 meters (490 ft) north of the Sylvan Bridge, it turns slightly southward (253°) and—300 m (980 ft) later—goes under the Finley-Sunset Hills building and water feature.  For the remaining 500 m (1,600 ft)), 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 (270°) about 500 m (1,600 ft) past the portals.
Robertson Tunnel