# List of tunnels in Seattle

This is a list of tunnels built in the city of Seattle, in the U.S. state of Washington.
The Puget Sound region, where Seattle lies, has a history of glaciation that has left many hills and ridges that civil engineers have needed to traverse for transportation and utilities. Some of these tunnels are part of megaprojects.

## Tunnels

| Year(s) Constructed | Tunnel | Diameter | Length | Notes |
| 1894 | Lake Union Sewer Tunnel | 72 in (1.8 m) | 5,736 ft (1,748 m) | Hand excavated |
| 1894 | South Bayview Street Tunnel | 4 ft (1.2 m) x 6 ft (1.8 m) | 4,526 ft (1,380 m) | Hand excavated |
| 1903–1905 | Great Northern Tunnel | 38 ft (12 m) | 5,141 ft (1,567 m) | Hand excavated |
| 1907 | Oregon and Washington Railroad Tunnel | 38 ft (12 m) | 900 ft (270 m) | Hand excavated; never completed (filled in 1922) |
| 1910 | First Avenue Utilidor Tunnel | 8 ft (2.4 m) | 300 ft (91 m) | Compressed air, hand |
| 1910 | 4th and Connecticut Ave. Sewer | 3–6 ft (0.91–1.83 m) | 7,060 ft (2,150 m) | Supported trench |
| 1910 | Ravenna Sewer Tunnel | 80 in (2.0 m) Relined 66 in (1.7 m) | 2,875 ft (876 m) | Hand; tried tunnel boring machine |
| Early 1900s | Wallingford Tunnel | 9 ft (2.7 m) | 1,803 ft (550 m) | Open cut and tunnel |
| Early 1900s | Pacific Street Tunnel | 9 ft (2.7 m) | 11,325 ft (3,452 m) | Open cut and tunnel |
| 1910 | Lander Street Sewer | 4.5–9 ft (1.4–2.7 m) | 5,290 ft (1,610 m) | Supported trench |
| 1911 | Fort Lawton Tunnel | 10 ft (3.0 m) | 9,720 ft (2,960 m) | Hand dug |
| 1911 | Montlake Siphon Tunnel | 4 ft (1.2 m) | 2,005 ft (611 m) | Hand dug |
| 1912 | Dexter and 8th Avenue Tunnel | 5 ft (1.5 m) | 9,315 ft (2,839 m) | Hand dug |
| 1912 | Washington Park Tunnels | 5 ft (1.5 m) | 4,052 ft (1,235 m) | Hand dug |
| 1913 | Third Avenue West Siphon Tunnel | 21 ft (6.4 m) | 500 ft (150 m) | Hand dug |
| 1926 | Jackson Street Drainage Tunnel | 4 ft × 6 ft (1.2 m × 1.8 m) | 1,500 feet (460 m) | Hand dug 35 psi compressed air |
| 1930 | South Hanford Street Tunnel | 9 ft (2.7 m) | 6,055 ft (1,846 m) | Hand dug |
| 1931 | Charleston Street Tunnel | 3.5 ft (1.1 m) | 2,830 ft (860 m) | |
| 1936 | Henderson Trunk Sewer Tunnel | 60 in (1.5 m) (I.D., concrete) 48 in (1.2 m) (brick) | 3,000 ft (910 m) | Hand dug Concrete and brick |
| 1936 | Laurelhurst Trunk Sewer Tunnel | 9 ft (2.7 m) | 1,850 ft (560 m) | |
| 1938–1941 | Mount Baker Tunnel | 28 ft × 23 ft (8.5 m × 7.0 m) | 1,330 ft (410 m) | |
| 1934–1942 | WPA slide control drainage projects | 4 ft × 6 ft (1.2 m × 1.8 m) | 4,926 ft (1,501 m) | |
| 1952–1954 | Battery Street Tunnel | | 3,140 ft (960 m) | Originally named Battery Street Subway |
| 1963 | Montlake Siphon Tunnel replacements | 42 in × 108 in (1.1 m × 2.7 m) | 586 ft (179 m) | |
| 1965–1966 | Elliott Bay Interceptor section 6 tunnel | 8 ft × 12.5 ft (2.4 m × 3.8 m) | 1,750 feet (530 m) | Tunnelling shield |
| 1964–1967 | Lake City Sewer Tunnel | 8 ft × 11 ft (2.4 m × 3.4 m) | 17,570 feet (5,360 m) | Close-face wheel excavator |
| 1967–1968 | Second Avenue Sewer Tunnel | 8.5 ft × 12.5 ft (2.6 m × 3.8 m) | 19,900 feet (6,100 m) | Tunnelling shield |
| 1960s to present | University of Washington utilidors | Various, 5–10 ft (1.5–3.0 m) | 50,000 feet (15,000 m) total | |
| 1975 | Northwest Kidney Center pedestrian tunnel | 10 ft (3.0 m) horseshoe | 120 ft (37 m) | Bobcat loader |
| 1983–1986 | Mount Baker Tunnel expansion | 65 ft (20 m) | 1,330 ft (410 m) | Tunnelling shield World's largest diameter soil tunnel |
| 1984 | Seattle Public Utilities Beacon Hill Waterline/Cedar River Pipeline | 12 ft (3.7 m) | 150 ft (46 m) | |
| 1985 | Columbia Center pedestrian tunnel | 14 ft (4.3 m) horseshoe | 280 ft (85 m) | |
| 1985 | Virginia Mason Hospital pedestrian tunnel | 10 ft (3.0 m) horseshoe | 120 ft (37 m) | Bobcat loader |
| 1986 | Renton Sewer Tunnel ETS-4A | 12 ft (3.7 m) O.D. | 2,403 ft (732 m) | Drill and shoot |
| 1986 | Renton Sewer Tunnel ETS-4B | 12 ft (3.7 m) O.D. | 620 ft (190 m) | Drill and shoot |
| 1986 | Renton Sewer Tunnel ETS-5 | 12 ft (3.7 m) O.D. | 1,820 ft (550 m) | Drill and shoot |
| 1986 | Renton Sewer Tunnel ETS-6 | 12 ft (3.7 m) O.D. | 1,056 ft (322 m) | First use of Earth Pressure Balance Machine in Seattle |
| 1987–1988 | Downtown Seattle Transit Tunnel | Twin 21.25 ft (6.48 m) | 13,624 ft (4,153 m) | Tunnelling shield First use of waterproofing PVC membrane in USA |
| 1990 | Fort Lawton Tunnel/West Point Sewer | 15.5 ft (4.7 m) O.D. | 8,400 feet (2,600 m) | Partial Earth Pressure Balance Machine |
| 1993 | Royal Brougham Street Sewer Tunnel | 10 ft (3.0 m) O.D. | 300 ft (91 m) | |
| 1993 | Lake Washington Canal Tunnel | 3.3 ft (1.0 m) | 1,518 ft (463 m) | First slurry microtunnel in Seattle |
| 1995 | Lander Street Sewer Tunnel | 10 ft (3.0 m) O.D. | 130 ft (40 m) | |
| 1995 | First Avenue Utilidor Tunnel | 10 ft (3.0 m) | 500 ft (150 m) | Microtunnel |
| 1995–1997 | West Seattle Sewer Tunnel | 13 ft (4.0 m) | 10,500 feet (3,200 m) | Partial Earth Pressure Balance Machine Maximum 400 feet (120 m) below surface |
| 1997 | Eastlake Storm Sewer Tunnel | 3.5 ft (1.1 m) | 475 ft (145 m) | Slurry microtunnel |
| 2001 | Justice Center Tunnel | 15 ft (4.6 m) horseshoe | 200 ft (61 m) | |
| 2002 | Denny CSO Storage Tunnel | 16.8 ft (5.1 m) O.D. | 6,212 ft (1,893 m) | First complete Earth Pressure Balance Machine tunnel in Seattle |
| 2002 | Henderson CSO Storage Tunnel | 16.8 ft (5.1 m) O.D. | 3,105 ft (946 m) | Earth Pressure Balance Machine, connecting microtunnels |
| 2006 | Beacon Hill tunnel | Twin 20 ft (6.1 m) | 1 mi (1.6 km) | Tunnel boring machine |
| 2009–2012 | University Link Tunnel | Twin 20 ft (6.1 m) | 3 mi (4.8 km) | Tunnel boring machine $1.9 billion megaproject |
| 2007–2011 | Brightwater Sewage Tunnel | 17.5 ft (5.3 m) | 13 mi (21 km) | Four tunnel boring machines Maximum depth 400 feet (120 m) Part of $1.8 billion megaproject |
| 2013–2018 | Alaskan Way Viaduct replacement tunnel | 57 feet (17 m) | 2 mi (3.2 km) | $4.25 billion megaproject World's largest tunnel boring machine, 57.5 feet (17.5 m) in diameter |
| 2014–2016 | Northgate Link tunnel | Twin 20 ft (6.1 m) | 3.4 mi (5.5 km) | Tunnel boring machine $2.1 billion megaproject |
| 2019– | King County Ship Canal Water Quality Project | 21.67 ft (6.61 m) and 8 ft (2.4 m) | 2.7 mi (4.3 km) | Largest tunnel boring machine named "Mudhoney" to construct combined sewer outflow storage tunnel under EPA consent decree. Two smaller machines for conveyance tunnels. |