Evergreen Point Floating Bridge (2016)

Evergreen Point Floating Bridge (2016)
Viewed from the east end in Medina shortly after opening in April 2016
Coordinates	47°38′27″N 122°15′33″W / 47.64080°N 122.25926°W / 47.64080; -122.25926Coordinates: 47°38′27″N 122°15′33″W / 47.64080°N 122.25926°W / 47.64080; -122.25926
Carries	6 lanes of SR 520
Crosses	Lake Washington
Locale	Seattle, Washington
Official name	The SR 520 Albert D. Rosellini Evergreen Point Floating Bridge[1]
Named for	Albert Rosellini
Owner	Washington State Department of Transportation
Characteristics
Design	Pontoon bridge
Material	Precast concrete
Total length	7,710 feet (2,350 m)
Width	116 feet (35 m) (at midpoint)
Design life	75 years
History
Construction cost	$4.56 billion (project budget)[2]
Dedicated	April 2, 2016 (2016-04-02)
Opened	April 11–25, 2016
Replaces	Evergreen Point Floating Bridge (1963–2016)
Statistics
Toll	$0–$5.55

The Evergreen Point Floating Bridge, also known as the 520 Bridge and officially the Governor Albert D. Rosellini Bridge, carries Washington State Route 520 across Lake Washington from Seattle to its eastern suburbs. The 7,710-foot-long (2,350 m) floating span is the longest floating bridge in the world,^[3] as well as the world's widest measuring 116 feet (35 m) at its midpoint.^[4]

The bridge opened in April 2016 and replaced another floating bridge of the same name at the site, which was 130 feet (40 m) shorter.^[4]

Background

The original Evergreen Point Floating Bridge, also named for state governor Albert D. Rosellini, opened on August 28, 1963, carrying the four-lane State Route 520 (at the time designated temporarily as the Evergreen Point branch of Primary State Highway 1 until the 1964 state highway renumbering).^[5] The 7,578-foot-long (2,310 m) floating span consisted of 33 pontoons and cost $24.7 million to construct (equivalent to $191 million in 2016);^[6] the bridge carried 4 lanes of traffic, separated by a curb that was later replaced with a simple Jersey barrier; at the center was a drawspan that opened for large vessels traversing the lake. The original bridge would also close to traffic during sustained wind gusts of 50 miles per hour (80 km/h) or higher for more than 15 minutes.^[5]

Due to increased traffic to and from the rapidly growing Eastside area, bridge replacement was explored as early as 1969, when building a parallel span was explored and rejected.^[7] The Eastside was also served prior to the 2016 bridge by the two Interstate 90 floating bridges completed in 1940 and 1989.^[8]

Planning and design

Planning of the replacement bridge started in 1997 with a cross-lake study conducted by the state Department of Transportation.^[9]:4 The study followed several others in the late 20th century to find solutions to traffic on the SR 520 floating bridge, with most proposals rejected after heavy opposition from communities on both ends of the bridge.^[10]

The final environmental impact statement for the project was issued in 2011, allowing for construction of the pontoons to begin the following year.^[11]

Funding

Funding was allocated to major phases of the project at different times. The western portions of the project, in the City of Seattle, were the last to be funded.^[9]:7 The $4.5 billion in funding comes largely from the state gas tax earmarked for highways, tolling, and Federal highway funds.^[2]

In 2014, the budget for the project was increased by $250 million to cover cost overruns.^[12]

Design elements

The new bridge was designed to be more stable in high winds and raised the bridge deck much higher above the surface of the lake than the old bridge. Unlike the original floating bridge, where the road surface is directly on pontoons connected end-to-end, the new bridge featured pontoons laid north–south, perpendicular to the direction of vehicular traffic, and a road surface on a platform raised 20 feet (6.1 m) above the water.^[4]

Pontoons and anchors

The floating bridge is laid atop 77 concrete pontoons that float above the water and are secured by 58 anchors to the lake bottom.^[13]

Of the pontoons, 21 are longitudinal pontoons that support the deck and structure and are 360 by 75 by 28 feet (109.7 m × 22.9 m × 8.5 m) and weight 11,000 short tons (10,000 t);^[4] 54 smaller supplemental pontoons, weighing 2,500 short tons (2,300 t), are used to stabilized the weight of the bridge; and two "cross" pontoons, weighing 10,100 short tons (9,200 t), are sited at each end of the floating span at transitional spans, which connect the deck to fixed bridges and approaches using hinges to move up to 24 inches (61 cm) for fluctuations in lake water levels moving the pontoons.^[13] All the pontoons are designed with watertight compartments that are monitored remotely with sensors to detect leaks that could lead to catastrophic failure.^[14]

The bridge's 58 anchors all feature 3-inch-thick (7.6 cm), 1,000-foot-long (300 m) steel cables and are divided into three types: 45 587-short-ton (533 t) fluke anchors used in softer soils deep in the lakebed; eight 107-short-ton (97 t) gravity anchors used in solid soils nearer to the shore; and five 10-foot-diameter (3.0 m), 79-to-92-foot-long (24 to 28 m) drilled shaft anchors used in conjunction with the gravity anchors to prevent navigation hazards.^[13][15]

Bridge deck

The bridge deck is made of 776 precast concrete sections that are elevated 20 feet (6.1 m) above the pontoons.^[4][14]

Layout

The bridge has two general purpose lanes and one high-occupancy vehicle lane (HOV lane) per direction. It includes shoulders and a 14-foot-wide (4.3 m) pedestrian/bicycle path on the north side, unlike the 1963 bridge.^[4] Congestion on the old bridge was blamed on lack of shoulders, where disabled vehicles would cause severe backups.^[16] Ornamental elements include four sentinel towers rising 43 feet (13 m) above the bridge deck at the approaches, and belvederes on the north side.^[4][17]

Public transportation

Public transportation and high-occupancy vehicle (HOV) use were incorporated in the bridge design. The bridge includes HOV lanes with priority for transit. A 2008 WSDOT report included five core bus rapid transit routes proposed by Sound Transit connecting the Eastside (Kirkland, Redmond, and Bellevue) to Downtown Seattle and the University District, with a base frequency of 15 minutes, increasing up to 7 minutes at peak times.^[18]:25–30

Existing freeway transit stations (also known as "flyer stops") on the Eastside at Evergreen Point and Yarrow Point were rebuilt and moved from the freeway's shoulder to the median, accompanied by landscaped lids with parking and lawns, in 2014 for increased compatibility with the bridge's planned HOV lanes.^[19]

The bridge was engineered to accommodate a Link Light Rail extension with two options (both requiring 30 additional pontoons): one option would be 116 feet (35 m) in width with two lanes each direction, plus light rail; the other 150 feet (46 m) in width with three lanes each direction (HOV), plus light rail.^[20]

Tolling

Electronic tolling with the "Good to Go" system on the old bridge began in 2011; tolling on the new bridge was in place from its opening in 2016. The tolls are projected to generate $1.2 billion by 2056, used to pay off bond issues for the project as well as bridge operations and maintenance, debt service, future repairs, insurance, and deferred sales tax.^[2]

Construction

New (left) and old (right) bridges in 2015 showing difference in decks: old road surface is directly on pontoons laid end-to-end, but new road surface is raised above pontoons laid perpendicular to road.

The first stage of the SR 520 floating bridge replacement project was the construction of 77 concrete pontoons in 2011 and 2012 by Kiewit-General at two purpose-built facilities in Aberdeen and Tacoma. The pontoons were floated to the bridge on Lake Washington via the Lake Washington Ship Canal.^[21][22] Pontoon assembly and fastening, to form the floating bridge's deck, began in 2014 and concluded in July 2015.^[23][24]

In 2012, WSDOT identified cracks and other problems with the first batch of completed pontoons, estimating that it would cost $400 million to repair cracks and other flaws that would bring down the bridge's predicted lifespan below the desired 75 years.^[25] The problems stemmed from shortcuts allegedly taken by contractors to complete pontoons to meet set deadlines; the proposed solutions to fix the pontoons included adding high-tension steel cables and post-tensioning of the concrete.^[26] A floating, 660-short-ton (600 t) cofferdam was launched in November 2013 to assist in repairs of the pontoons, functioning as a portable drydock that wrapped around parts of the pontoons.^[27] The repairs were made by contractors from December 2013 to June 2014 and cost a total of approximately $208 million,^[28] using up the majority of the program's reserve funds.^[29][30] As a result of the pontoon issues, the estimated opening of the bridge was pushed back from December 2014 into 2016.^[26][29]

Construction of the bridge deck, beginning with the eastern approach in Medina, began in March 2012.^[17][31]

In March 2015, two construction accidents on the bridge slowed construction for reevaluation of safety measures: a contractor was killed after a high fall on the east highrise; and a crane-lifted load of steel pipes swung out of control into a King County Metro bus and an overhead highway sign.^[32]

The bridge deck was lifted into place in August 2015,^[33] and the final concrete pour was finished in October 2015, completing the bridge deck.^[34]

Opening

New Evergreen Point Floating Bridge has been in use since April 2, 2016.

The new bridge was dedicated on April 2, 2016, in a ceremony presided over by Governor of Washington Jay Inslee. The ceremony also included a community marathon and walk on the bridge, and a bicycle ride hosted by the Cascade Bicycle Club on the bridge and the Interstate 5 express lanes the following day.^[35] As part of the opening ceremonies, the bridge was certified as the world's longest floating bridge by Guinness World Records, at 7,708.49 feet (2,349.55 m) long;^[36] the bridge took the record from the previous Evergreen Point Floating Bridge, which is 130 feet (40 m) shorter in length.^[37]

Traffic on the new bridge was shifted over in two stages, beginning with westbound traffic on April 11 and ending with eastbound traffic on April 25.^[38][39] Initially, the bridge will narrow from 6 lanes to 4 lanes at the end of the floating span, over 1.2 miles (1.9 km) east of the Montlake Boulevard interchange, and not be fully traversable for bicyclists and pedestrians; the new westbound approach bridge is scheduled to be open in the summer of 2017.^[40][41] The bridge's multi-use bike and pedestrian path partially opened in July 2016, with access to the completed sections for an "out-and-back" experience.^[42]

Shortly after the opening of the bridge's westbound lanes, the Washington State Transportation Commission proposed increasing toll rates to introduce nighttime tolling by 2017.^[43]

The old bridge was planned to be decommissioned by floating away pontoons to an industrial site in Kenmore for disposal and recycling;^[44] in March 2016, the city rejected the plan, citing the possible release of toxins in the pontoon's concrete.^[45] The pontoons were sold to a recycling company based in Gig Harbor which plans to reuse the individual pontoons for floating decks and other projects.^[46] An unaffiliated contest was held in 2012 seeking ideas for the 33 pontoons of the old bridge, with solutions ranging from a "floating High Line" to partial submersion for walking paths.^[47] The first pontoon of the old bridge to be disassembled was towed through the Lake Washington Ship Canal in July 2016.^[48]

References

External links

• SR 520 Bridge Replacement and HOV Program
• SR 520 Project Library