Downtown Seattle's narrowness had prompted a long search for ways to expedite the flow of transit vehicles, especially buses traveling through the downtown from suburban communities. In the early 1980s, Metro Transit planners proposed terminals north and south of downtown linked by an electric transit mall down Third Avenue.
This would reduce downtown bus traffic and pollution, but also force suburban riders to change vehicles even if they were just passing through. Eastside leaders such as Kirkland City Council Member Robert Neir and King Council Member Paul Barden objected strongly, creating a stalemate with Seattle officials.
In the fall of 1983, Metro director Neil Peterson proposed a compromise: run "dual-mode" electric-diesel buses through a downtown tunnel from 9th Avenue at Pike Street to Union Station at 5th Avenue and S Jackson St. This got diesel buses off downtown streets and didn't require suburban riders to transfer, but it also created a very expensive and technically challenging project.
Peterson retired soon after winning local agreement to the tunnel, and Alan Gibbs took charge of Metro while David Kalberer guided project planning by Parsons Brinkerhoff and TRA architects and engineers. The project entailed the boring of two parallel tubes 60 feet beneath city streets, five distinct transit stations, and relocation of existing utilities. At the suggestion of Seattle City Council Member George Benson, planners also added rails for future light rail (but these would later prove inadequate).
Unfortunately, tunnel excavation coincided with a major boom in downtown office building construction and helped to create a three-year-long traffic jam. Rising costs, second thoughts, and downtown complaints bedeviled the project from the outset, but construction itself proceeded relatively smoothly. Progress was marred by encounters with unanticipated soil conditions, one fatal construction accident (killing Alan Sandbow), and a racially charged scandal over the inadvertent use of banned South African marble that ultimately led to Gibbs's resignation. The first of 236 dual-mode buses also proved to be overweight (at nearly 25 tons each) and prone to breakdowns.
Despite these obstacles and distractions, the downtown tunnel was completed on schedule. Primary excavation was completed in the spring of 1988, the first bus tested the tunnel on March 15, 1989, and the flagship Westlake Station opened for public inspection on August 11, 1989. The airy stations and their distinctive artworks, coordinated by Jack Mackie, impressed even the skeptics.
Regular bus service in the tunnel began on September 15, 1990. After 15 years, the tunnel was closed on September 24, 2005, to be retrofitted for use by light rail (in addition to buses) as part of Sound Transit's plan to build a light rail system from downtown Seattle to Sea-Tac International Airport. Although rails were included when the tunnel was first built, they weren't insulated adequately to prevent stray electric current from trains from corroding nearby utility lines. As correcting this required removal of the original rails, Sound Transit also took this opportunity to lower the tunnel roadway to allow level train boarding.