New Bridge Approach on Lake Washington Marks Latest Phase in WSDOT SR 520 Program
State Route 520 in Washington is one of the Puget Sound region's busiest highway corridors, economically important to the city of Seattle and other cities, where every day tens of thousands of people take this route across Lake Washington. With its far-reaching SR 520 Bridge Replacement and HOV Program, the Washington State Department of Transportation (WSDOT) is making major enhancements to this vital corridor, improving traffic safety by replacing aging and vulnerable bridges, and making other key highway improvements to public mobility and transportation options.
Following years of public discussion, planning, design and engineering work (studies began in 1997), construction along the 12.8-mile SR 520, which extends from I-5 in Seattle to SR 202 in Redmond, began in 2011 and is proceeding in separate, phased, primarily design-build projects. The $4.5 billion program was designed to address multiple needs along the route, reports WSDOT SR 520 Director of Construction Dave Becher.
"The overall goal of the program is to bring the whole corridor up to current standards," says Becher. "Much of the highway dates from the late 1950s and early 1960s, and was not up to modern seismic standards. The old four-lane floating bridge on Lake Washington, which was built over 50 years ago, was very susceptible to winds and weather; we've replaced it with a longer, safer, six-lane bridge designed to withstand strong windstorms and waves. The program will also add an HOV lane along the whole length of the route, and all pavement is being updated."
New Bridge Approach, New Pedestrian Path Part of Latest Phase
The SR 520 program's latest phase is the construction of the West Approach Bridge North Project (WABN); this new bridge is expected to open to traffic this summer. The three-lane, 1.2-mile-long structure replaces one of the corridor's vulnerable elements, and will connect westbound travelers from the recently completed new floating bridge to the city's Montlake area. (Traffic counts over the existing bridge averaged 70,000 to 80,000 vehicles daily.)
The project will also connect a new, 14-foot-wide bicycle/pedestrian path, expanding travel options to local and regional destinations, and extend a new transit/HOV lane to support bus and carpool reliability.
WSDOT awarded a $199.5 million contract to Flatiron West, Inc. to construct the WABN, which is fully funded after WSDOT received a $300 million federal loan. The primary design/general engineering consultant was HDR Engineering, Inc. Construction on the bridge project began in the fall of 2014; a previous project completed was an interim bridge designed to connect the new floating bridge on Lake Washington to the existing west approach bridge. The new floating bridge itself opened to traffic in April 2016. When WABN opens to traffic this summer, westbound traffic will travel on the new structure while eastbound traffic will travel on the existing west approach. Eastbound traffic will continue to use the existing west approach structure during WABN construction, but will ultimately travel on a new West Approach Bridge South; construction on that phase will begin at a later date.
Additionally, as a result of WABN construction, SR 520's new bicycle and pedestrian path will extend from Montlake across Lake Washington to the Eastside, with connections to local and regional trails on both sides of the lake. The West Approach Bridge North project also will implement local street improvements in the Montlake area, and a wider bicycle/pedestrian path on 24th Avenue East in Montlake.
Strong Focus on Safety and Environmental Enhancement
Safety has been a prime consideration in the design and construction of the new West Approach Bridge. As WSDOT spokespersons point out, the old bridge is a fixed structure, and the hollow columns supporting it are vulnerable to a catastrophic earthquake. Additionally, its four-lane roadway has narrow shoulders and no transit/HOV lanes or bicycle/pedestrian path. In contrast, the new bridge is being built to modern seismic codes. The new floating bridge, meanwhile, was built to withstand windstorms that used to shut down the old floating bridge. The new west approach bridge includes solid columns that can withstand earthquakes. (If the aging south/eastbound half of a new west approach bridge structure were to fail in a severe earthquake before its replacement can be built, the new West Approach Bridge North will have the width to support four lanes of traffic in an interim configuration). The new design also includes shoulders where disabled vehicles can pull out of traffic and emergency vehicles can reach accidents.
Meeting the needs of all the stakeholders in the project has also been a major focus throughout the WABN planning process. Once a baseline design for the project was federally approved, WSDOT convened the Seattle Community Design Process to hear from the public, agency partners, and design professionals, including the Seattle Design Commission (SDC). The agency also collaborated with the city of Seattle through technical working groups focused on WABN design refinements.
Becher explains, "There has been very extensive outreach to the public. We wanted the design to meet the needs of the traveling public and at the same time correct some of the troublesome design aspects of the old bridge and its impact on the adjacent neighborhoods. There are some very large homes, and some historic neighborhoods, in the area."
Particular emphasis has been placed on environmental enhancements around the Washington Park Arboretum, established in 1934; its 230 acres on the shores of Lake Washington feature a wide assortment of plants, some of which are found nowhere else in the Northwest. SR 520 currently has a set of what are locally called "ramps to nowhere" within the Arboretum. One ramp is currently used for the on-ramp to SR 520 eastbound. The others, some completely unused, were originally part of a plan to build an expressway which would have cut through the Arboretum. Citizen resistance to this plan in the late 1960s ultimately led to its abandonment.
Removal of this group of ramps has been part of the SR 520 program plans for several years, and WSDOT has worked closely with the Arboretum, Seattle Parks, and other community partners. "Removing the ramps will result in additional open space in the Arboretum and reduced traffic noise in the area, and aid the Arboretum in its environmental and plant restoration efforts," comments WSDOT's Jon Vannoy, the WABN Assistant Project Engineer. "A new multi-use Arboretum trail is also part of the Program's efforts to restore the area."
Meeting the Challenges of a Complex Project
Certainly, the complex West Approach Bridge North project has presented challenges, as Steve Strand, the Project Engineer, points out. "The majority of the bridge being built is over water, but a temporary trestle allowed the use of existing ramps and made for shorter haul routes, so the construction didn't impact the main 520 route as often as it could have. Montlake Boulevard is very congested, and carries a lot of traffic to the sports arenas, so that required a lot of coordination with city traffic engineers."
Adds Becher, "This project has required a lot of demolition, and we have strived to not let any material into the water."
The public was provided with advance notice of highway closures and lane closures on local streets, report the WSDOT spokespersons, and highway closures were limited to nights and weekends to keep weekday traffic flowing. Regular bus service has been maintained throughout the entire construction period, and a navigation channel has remained open for boaters on Lake Washington.
The WABN project is also emphasizing sustainable practices to minimize the effects of construction. WSDOT worked closely with the Seattle Design Commission to refine the design and reduce concrete volumes by nearly 50 percent. The next phase of construction will feature a new constructed storm water wetland that will filter the highway runoff water, which currently flows untreated into Lake Washington.
The SR 520 Bridge Replacement and HOV Program (which has at least three more phases in the planning stages) will continue to enhance public safety and mobility along a vital Washington State corridor. The West Approach Bridge North Project will provide extensive benefits to travelers along the route: a new, seismically sound structure designed to modern earthquake standards; new transit/HOV lanes; enhanced bicycle and pedestrian connections; and environmental improvements to the surrounding neighborhoods and recreational areas.
As Strand comments, "The seismic upgrades to modern standards, the new shared-use path, and the Arboretum ramp removals are all going to be huge benefits. A lot of people are drawn to this part of the state because of the environmental diversity and economic opportunities, and from one end to the other, the SR 520 program is bringing about some very positive transformations."