and 71,000 vehicles between Columbia Street and Western Avenue. The viaduct formerly carried an average daily volume of 110,000 vehicles until the start of demolition in 2011. The viaduct and other sections of SR 99 were designated as part of the National Highway System by the federal government and as Highway of Statewide Significance by the state legislature. History The Alaskan Way Viaduct was originally built to carry a section of U.S. Route 99, the main north–south highway in Washington and along the U.S. West Coast. The highway previously used downtown streets, but rising automobile congestion in the 1920s sparked proposals for a limited-access bypass of Seattle. An elevated roadway, placed along the waterfront's Railroad Avenue (later renamed Alaskan Way), was recommended by several city engineers in the latter part of the decade. Plans for an elevated highway gained public support in the late 1930s and was approved for construction in 1947 using funds from the Federal-Aid Highway Act of 1944. Construction on the viaduct began in February 1950 and was completed in stages between 1953 and 1959. The central portion, from Railroad Way to Elliott Avenue, opened on April 4, 1953. It was connected to the Battery Street Tunnel the following year and a series of offramps and onramps to downtown in the 1960s. Additional ramps to University and Spring streets were included in design plans, but never built. The southern section of the viaduct, linking to the Spokane Street Bridge, was opened in September 1959. The viaduct officially closed on January 11, 2019, attracting spectators and drivers who caused it to miss the 10 p.m. deadline. Demolition of the northbound ramp on Railroad Way began the following day in preparation for the excavation of pre-constructed ramps into the new tunnel. Demolition was completed in stages between February and November 2019, using a section-by-section approach to avoid major disruptions. The last section to remain standing was near Pike Place Market. Replacement project Earthquake concerns The 1989 Loma Prieta earthquake destroyed the similarly designed Cypress Street Viaduct in Oakland, California, with the loss of 42 lives. The 2001 Nisqually earthquake damaged the viaduct and its supporting Alaskan Way Seawall and required the Washington State Department of Transportation (WSDOT) to invest US$14.5 million in emergency repairs. Experts gave a 1-in-20 chance that the viaduct could be shut down by an earthquake within the next decade. Semi-annual inspections discovered continuing settlement damage