The Mount Baker Tunnel or Mount Baker Ridge Tunnel carries Interstate 90 under the Mount Baker neighborhood of Seattle, Washington. It is actually a group of four tunnels that carry eight lanes of freeway traffic, plus a separate tunnel for bicycles and pedestrians. The two originals are twin tunnel bores completed in 1940 and rehabilitated in 1993. Two double-decked tunnels and the bicycle/pedestrian tunnel were built north of the original tunnels in 1991.
At 63 feet (19 m) in diameter, it is the world's largest diameter soft earth tunnel, having been bored through clay.
Mount Baker Tunnel
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