In 1903, a one-mile-long tunnel below downtown Seattle from Alaskan Way on the waterfront to Fourth Avenue South and Washington Street was built by Great Northern Railway. The construction costs were split by Great Northern and the Northern Pacific.
Work began on April 4, 1903; 350 laborers with picks, shovels, and wheelbarrows started digging from the Northern and the Southern portals. Along the dig they came across blue clay and hard gravel formations that required drilling. During the excavation, water seepage plagued the diligent crews.
Nonetheless, the two tunnels were connected on Oct. 26, 1904. Two months later, the tunnel was complete and ready for train traffic. It was not used, however, until completion of the King Street Station in May 1906. It was 28 feet high 30 feet wide, lighted by electricity, ventilated and large enough for a double line of tracks.
The cost in 1904 money was $1.5 million, with $500,000 spent on materials and other costs.
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