State Route 99 tunnel
The State Route 99 tunnel, also known as the Alaskan Way Viaduct replacement tunnel, is a bored highway tunnel in the city of Seattle, Washington, United States. The, double-decker tunnel carries a section of State Route 99 under Downtown Seattle from SoDo in the south to South Lake Union in the north.
Since the 2001 Nisqually earthquake, the replacement of the Alaskan Way Viaduct had been the source of much political controversy demonstrating the Seattle process. Options for replacing the viaduct, which carried 110,000 vehicles per day, included replacing it with a cut-and-cover tunnel or a bored tunnel, replacing it with another elevated highway, or eliminating it while modifying other surface streets and public transportation. The current plan emerged in 2009 when government officials agreed to a deep-bore tunnel.
Construction began in July 2013 using "Bertha", at the time the world's largest-diameter tunnel boring machine. After several delays, tunnel boring was completed in April 2017, and the tunnel opened to traffic on February 4, 2019.
Description
The SR 99 tunnel is a single tube that measures long and wide, carrying a double-decker highway that is wide and has two lanes in each direction. Each deck has two lanes, an west shoulder, and a east shoulder. The decks are designed with banks of two degrees in turns and four-degree grades to facilitate designed speeds of. Below the highway decks are utility lines and mechanical spaces for the tunnel's ventilation, lighting, and fire suppression systems.The tunnel has 15 emergency refuge areas located every with escape routes that lead to the north and south portals. Variable message signs and emergency phones are also located throughout the entire tunnel. The tunnel is monitored by over 300 security cameras that are fed into a WSDOT traffic control center in Shoreline that can dispatch incident response teams. In the event of a fire, a set of fiber optic cables in the ceiling would sense heat and activate sprinklers. A set of large fans located in the two portal operations buildings would then force smoke out through a set of ventilation shafts. The tunnel also has repeaters for cell phone and FM radio service; WSDOT can override the latter for emergency broadcasts.
Route
The tunnel begins south of Downtown Seattle in the SoDo neighborhood, adjacent to the Port of Seattle's container ship terminal and the city's two outdoor sports stadiums, Lumen Field and T-Mobile Park. SR 99 enters the tunnel after passing Royal Brougham Way and an interchange with Alaskan Way at South Dearborn Street located adjacent to the south maintenance area and ventilation shaft. An additional set of ramps connect to South Royal Brougham Way and Colorado Avenue South, which terminates a block south at South Atlantic Street. The tunnel carries two lanes of southbound traffic on its upper deck and two lanes of northbound traffic on its lower deck, and functions as a complete bypass of Downtown Seattle with no intermediate exits; it has a posted speed limit of.The tunnel travels northwesterly under Pioneer Square and Downtown Seattle, generally following 1st Avenue. It reaches its deepest point at Virginia Street, approximately below street level, and begins its turn north through parts of Belltown and the Denny Triangle. The tunnel emerges at a portal located west of Aurora Avenue and north of Harrison Street, adjacent to a tunnel operations building. SR 99 continues onto Aurora Avenue and crosses over Mercer Street, while an onramp allows access to the tunnel from 6th Avenue and an offramp carries tunnel traffic to Republican Street in South Lake Union.
Tolls
The SR 99 tunnel is tolled with a variable rate that changes based on time of the day, number of vehicle axles, and payment method. Tolls are collected electronically, with a lower rate for Good to Go pass users and a higher rate for scanned plates that are sent a bill in the mail. Tolling began on 9 November 2019, with the rate for two-axle vehicles set at $1.20 to $2.70 for Good to Go users and $3.20 to $4.70 for pay-by-mail users. The start of tolling was delayed by several months due to vendor issues and the viaduct demolition running behind schedule. Toll collection is expected to yield $22 million in annual revenue, which will cover 6 percent of the construction costs of the tunnel megaproject and its debts; the toll-collection vendor will be paid $16 million for system setup and $29 million over a five-year period. Beginning in 2022, the toll rates will increase by three percent annually with approval from the state transportation commission.Planning history
Viaduct and earthquake risks
The Alaskan Way Viaduct was a double-decked elevated freeway that ran along Elliott Bay on the Downtown Seattle waterfront and, until January 11, 2019, when it was permanently closed, carried a section of State Route 99. It first opened to traffic on April 4, 1953, to provide a vehicular bypass of downtown for U.S. Route 99, the predecessor of SR 99; it connected with the Battery Street Tunnel, which opened the following year, and several downtown ramps that were completed years later. The viaduct and tunnel cost $18 million to construct and severed the waterfront from the rest of downtown.The viaduct remained the primary north–south highway in Downtown Seattle until the construction of Interstate 5 in the late 1960s. Weekday traffic volumes on the viaduct averaged around 110,000 vehicles per day in the mid-2000s, approximately half of equivalent sections on I-5. Calls to replace the viaduct and build a waterfront promenade surfaced as early as the late 1960s and early 1970s, increasing after the halted demolition of the Pike Place Market. The viaduct runs above the surface street, Alaskan Way, from S. Nevada Street in the south to the entrance of Belltown's Battery Street Tunnel in the north, following previously existing railroad lines.
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 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 following decade. After the Nisqually earthquake, the viaduct was closed twice a year for WSDOT to conduct inspections of the structure. Those inspections discovered continuing settlement damage. In 2005, a group of researchers and faculty from the University of Washington urged political officials to close the viaduct within a two-year timeframe.
Options and political debate
Several replacement proposals were developed. Many Seattle leaders, including then-Mayor Greg Nickels and state and city transportation officials, favored building a tunnel. Plans for a six-lane, "cut-and-cover" double-decker tunnel were developed. The tunnel was envisioned to solve not only the viaduct's traffic limitations and safety problems, but also to allow better uses for the waterfront real estate, including parks, housing, and retail developments. While future development of the Alaskan Way real estate corridor may provide tax revenue for the city, many state lawmakers objected to the cost of the proposed six-lane tunnel. One criticism compared the plan to Boston's Big Dig project, which was said to illustrate the schedule and budget challenges of a large cut-and-cover tunnel. Proponents responded that the Seattle proposal was significantly smaller in scale than the Big Dig.Another proposal aimed to replace the current viaduct with another elevated structure with updated seismic standards. This new viaduct would be larger, wide lanes with new shoulders on both sides, compared to the structure it would replace, which had no shoulders and lanes as narrow as in places. The on and off ramps at the northern and southern portion of the viaduct would remain the same with an additional full intersection at South Atlantic Street and South Royal Brougham Way. The First Avenue off ramp would be removed. The plan included a complete replacement of the sea wall. It was estimated to cost $2.8 billion and take 10–12 years to construct. Many prominent leaders and organizations opposed the elevated structure and believed this was a unique opportunity to remove the viaduct and connect downtown Seattle to the waterfront. Former Governors Dan Evans and Gary Locke, former U.S. Senator Slade Gorton, and the American Institute of Architects recommended against rebuilding the viaduct.
WSDOT evaluated five proposals in 2003–2004 and decided that the six-lane cut-and-cover tunnel was the preferred alternative. Rebuilding the viaduct was retained as a backup plan.
However, due to the costs and scope of the project, other options were still being discussed in the local media. A proposal to remove the viaduct and replace it with surface street and transit improvements was backed by former King County Executive Ron Sims, the People's Waterfront Coalition, and the Congress for the New Urbanism. Proponents of this plan offered examples of successes in removing highways in other cities. They envisioned the waterfront becoming a pedestrian-friendly neighborhood with a mix of commercial, retail, and public park spaces. Traffic needs would be addressed through modifications to existing streets, I-5, and public transit; they argued that these modifications would be desirable in any event. Proponents further argued that this plan had the potential to improve the tourist economy, create jobs, and encourage a denser and more residential downtown through the offering of a generous waterfront park. The total cost of removal of the viaduct, repairing the seawall, and improvements to I-5 and existing streets was unofficially estimated to be $1.6 billion. In 2006, Seattle City Council member Peter Steinbrueck noted, "While the mayor's first choice is the tunnel, he supports the City Council's resolution that designates a surface and transit alternative as a backup."
In response to concerns about the cost of the originally proposed tunnel construction, the city council created a scaled-down, four-lane hybrid tunnel option. This would have combined the smaller tunnel with surface transit improvements to address traffic needs. The tunnel's shoulders would be used as an extra travel lane each way during periods of high demand. Transit service would be increased during peak commuter periods. Cars entering and exiting from Elliott and Western Avenues would each have a dedicated lane. Third Avenue would become a permanent transit corridor. The cost estimate for the four-lane tunnel was $3.4 billion. On February 13, 2007, Governor Christine Gregoire rejected the tunnel hybrid option, saying that a WSDOT review showed the tunnel proposal "does not meet state and federal safety standards." Of particular concern was that the use of shoulders as traffic lanes during peak traffic times would leave no additional lanes for emergency access. However, several of the viaduct "stakeholders committee" brought on board to advise the city indicated that the tunnel option should remain on the table.
State and city officials deadlocked in late 2006 over whether to build an elevated structure or a hybrid tunnel. Governor Gregoire stated "no action" was not an option for the viaduct. The state government called for an advisory ballot on March 13, 2007, for Seattle residents, which was supported by the city council. The advisory ballot allowed Seattleites to vote on whether they supported a surface-tunnel hybrid and whether they supported an elevated structure. Voters rejected both options, with the surface-tunnel hybrid getting only 30% support and the elevated structure only 43%.
Mayor Mike McGinn, elected in 2009 and opposed to highway expansion, joined other tunnel opposition groups to refer city council-approved agreements about the tunnel to the voters as a citizen's referendum. The referendum was initially blocked by a lawsuit from the city, but was pared down to one aspect of the city's approval for the project and placed on the August 2011 ballot. Under the ruling, the referendum would only challenge one section of the original 140-page City Council ordinance that approved agreements over street use, utilities, design and liability for the tunnel following completion of the project's ongoing environmental review process. The referendum vote approved the City Council's actions by 58 percent on August 16, 2011. The Federal Highway Administration completed its analysis of the project's final EIS and issued its record of decision with WSDOT later that month, allowing pre-construction activities to begin.