Consider this. What if the very ground beneath your feet could tell a story? The Mount Baker Ridge Tunnel does just that. It whispers tales of innovation and perseverance.
This isn’t just a tunnel. It’s a trio of tunnels. They carve through the Mount Baker neighborhood. These tunnels carry Interstate 90. They also provide a path for bikes and pedestrians. The Mount Baker Ridge Tunnel stands as a testament to Seattle’s ingenuity.
The original twin tunnels emerged in 1940. They were then updated in 1993. A new tunnel joined them to the north in 1989. It created a double-decked roadway. The bicycle and pedestrian path sits above the traffic lanes.
Listed on the National Register of Historic Places since 1982, the Mount Baker Ridge Tunnel has a unique distinction. Its east portals showcase murals by James FitzGerald. Titled Portal of the North Pacific, they are an official City of Seattle landmark. They stand alongside the Lacey V. Murrow Bridge.
Officially, the Mount Baker Ridge Tunnel stretches 1440 feet. Driving through it feels longer almost 3300 feet. This is because of a cut-and-cover “lid.” It extends from the west portal. This lid bridges the gap before the actual tunnel under Mount Baker ridge. The old west portal is now hidden well inside. Its arches vanished during the 1989-1993 renovations. The east end connects to the Lacey V. Murrow and Homer M. Hadley Memorial Bridges. Together, they form the I-90 floating bridge to Mercer Island.
Did you know the Mount Baker Ridge Tunnel boasts a record? At 63 feet in diameter, it’s the world’s largest soft earth tunnel. It was bored through clay.
Originally, the twin tunnels linked the I-90 floating bridge and Rainier Avenue South. They were part of US Highway 10. Each tunnel had two lanes. Lane-use signals appeared in the 1960s. They managed peak commute traffic by reversing the center lanes.
The 1983-1993 expansion brought a new parallel tunnel. It sits north of the originals. When completed in 1993, the 1940 tunnels became eastbound only. The 1989 tunnel became westbound only.
The new tunnel handles traffic on three levels. The bottom level has two lanes for buses and carpools. The middle level offers three lanes for general traffic. Cyclists and pedestrians enjoy the top level.
When the new tunnel first opened in 1989, it carried all traffic temporarily. This allowed work on the old Mercer Island Bridge. The old tunnel and floating bridge closed for renovation. A storm in 1990 caused a section of the Murrow Bridge to sink. The reopening was delayed until 1993.
Upon the Murrow Bridge’s 1993 reopening, the older Mount Baker Ridge Tunnel also reopened. All lanes became eastbound. Pedestrians were no longer allowed in the older tunnels. The new tunnel provided exclusive facilities for them. Concrete barriers now separate reversible lanes in the newer tunnel. This enhanced safety.
The I-90 expansion more than doubled the tunnel’s length. A 2000-foot concrete lid now covers the freeway. It extends from the old west portal. The inside of the older tunnels was reshaped. It matched the “lidded” section. Equipment was added to boost radio reception.
Today, the Mount Baker Ridge Tunnel facilitates three general-purpose lanes in each direction. Two reversible HOV lanes also exist. Eastbound traffic uses the original tunnels. Westbound traffic flows on the upper deck of the 1989 tunnel. The lower deck contains a two-lane reversible roadway.
Above the westbound traffic lies the I-90 Trail tunnel. It stretches 1330 feet. It is the world’s longest non-adapted trail tunnel.
The Mount Baker Ridge Tunnel is more than concrete and asphalt. It is a symbol of Seattle’s innovation. It showcases the city’s ability to adapt and expand. As you pass through this marvel, remember the history beneath you.