Bay Freeway (Seattle)

The Bay Freeway, also referred to as the Mercer Street Connection, was a proposed elevated freeway in the South Lake Union neighborhood of Seattle, Washington. The 0.7-mile-long (1.1 km) freeway would have run parallel to a section of Mercer Street between Interstate 5 (I-5) and Aurora Avenue North at the Seattle Center.

Planning for the freeway began in 1954, with the proposal for a freeway from Elliott Bay to the Central Freeway, later I-5, via Broad and Mercer streets added to the city's comprehensive plan in 1957. Funded by a bond measure passed by Seattle voters in 1960, plans were drawn for the newly renamed Bay Freeway to serve a multi-purpose stadium at the Seattle Center via an elevated structure.

Citizen groups voiced their opposition to the project at public hearings in 1967, forcing the Seattle Engineering Department to consider other designs. After determining that a cut-and-cover tunnel would not be feasible, a second series of public hearings to discuss the impact of an elevated option were held in 1970, leading to widespread controversy and a civil suit launched in opposition to the freeway. The lawsuit ended in November 1971, with a King County Superior Court judge ruling that a major deviation from the voter-approved 1960 plan occurred, forcing a referendum to be held on whether to continue the project.

On February 8, 1972, the Bay Freeway project was rejected by a 10,000-vote margin in a municipal referendum, alongside the repeal of the R.H. Thomson Expressway. Mercer Street would later undergo several projects that attempted to provide congestion relief promised by the rejected freeway, culminating in the Mercer Corridor Project in 2012, which widened the street into a boulevard.

The 0.7-mile-long (1.1 km) Bay Freeway, as proposed in 1972, would have been a six-lane elevated freeway on a curved box-beam bridge, measuring 180 feet (55 m) at its widest point. The freeway would have begun at the Seattle Center in Lower Queen Anne, as through lanes for Broad Street under Aurora Avenue North. The roadway would have immediately merged with ramps connecting to the Roy and Mercer couplet and to a parking garage for a multipurpose domed stadium, later relocated and built south of Downtown in 1976, to form the Bay Freeway. The lanes then would have then turned southeastward next to a park on Lake Union, passing only 16 feet (5 m) over Westlake Avenue North and 25 feet (8 m) over Fairview Avenue North, before splitting into ramps at an interchange with I-5. Valley Street, located 175 feet (53 m) north of the planned right-of-way, was to be moved under the Bay Freeway structure and replaced with additional park space.

Earlier plans called for an extension traveling southwest on Broad Street through Belltown, including a tunnel between 5th Avenue and Denny Way, to the proposed Northwest Expressway and an extension of the existing Alaskan Way Viaduct on the Elliott Bay waterfront. The extension was deferred in 1969, but remained a "possible future plan" until the entire project was canceled.

The City of Seattle began planning for the Bay Freeway in 1954, with planning studies determining that Broad and Mercer streets should become the northern east–west link of the proposed Downtown freeway system. The Seattle City Council adopted the city's comprehensive plan in 1957, proposing a "major highway" in the vicinity of Broad and Mercer streets from the Northwest Expressway along Elliott Bay to the Central Freeway at the foot of Capitol Hill. In anticipation of the Bay Freeway, underpasses of Aurora Avenue North on Broad and Mercer streets were completed in July 1958, using funds from a 1954 bond issue for the construction of arterial roadways. A special municipal election concerning a $26.6 million bond measure (equivalent to $215 million in 2024 dollars) for traffic improvement was held on March 8, 1960, passed by 71,000 of 109,000 voters in King County. The funds, matched by $31 million (equivalent to $251 million in 2024 dollars) from the State of Washington and federal government, were distributed to 12 projects from the Comprehensive Plan of 1957, including $1.9 million (equivalent to $15.4 million in 2024 dollars) for the "Mercer Street Connection" between Aurora Avenue and the Central Freeway.

The Century 21 Exposition was hosted at the Seattle Center grounds from April to October 1962, generating heavy traffic equivalent to rush hour loads on Mercer Street, where a city-owned, 1,500-stall parking garage was located. The use of Mercer Street as one of the primary routes to the fairgrounds and its selection as one of the sites for a proposed multi-purpose stadium convinced city officials that the construction of the Bay Freeway was a necessity. The Mercer exit on I-5 was partially opened in November 1963, with the northbound ramps open to traffic and the southbound ramps remaining closed until 1968. A design team led by Perry Johanson was formed in 1966 for the Bay Freeway project, intending to blend the freeway with its surroundings and encourage mixed-use development to lower its impact on the South Lake Union neighborhood. The first public hearing on the project was held by the Seattle City Council on February 17, 1967, where City Engineer Roy Morse said that the "Mercer mess" would be solved with the opening of the Bay Freeway in 1969. The three proposed elevated alternatives were criticized by the public and local architects Ibsen Nelsen and Victor Steinbrueck for blocking views of Lake Union, forcing Morse to reconsider subsurface designs despite his declaration that "a depressed roadway with the freeway would require excessively steep traffic grades".