Seattle’s Sound Transit aspires to make an infrastructural breakthrough by building a train track on a floating bridge. The one mile rail road will serve as the East Link light rail line by 2023 carrying four trains weighing 300 tonnes each. Sound Transit is the regional transit authority for the Seattle region in Washington and plans to operate a new network between Seattle, Bellevue and Overlake. However, this is not a simple operation – there is a reason that this hasn’t been done before. It will be difficult to adapt the rail to the movement of the bridge with the rise and fall of the lake levels. Nevertheless, the project has been approved by voters to provide 14 miles of rail to the Eastside of Seattle to make a 15 minute commute from Bellevue into downtown Seattle. Under normal conditions, it is predicted that trains will be able to travel at speeds of around 55mph serving a ridership of 50,000 a day.
Seattle will begin works next month on the $3.7 billion project. In order to bring the project from plan to reality, the transit agency will use earthquake-proof technology to adhere to rigorous safety regulations.
According to the Seattle Times: “A derailed train would sink 200 feet to the lake bed. If track components break or wear out, transit service would be halted for maintenance, or subjected to slowdowns.”
Fortunately, the transit agency will not be working from a blank page with Seattle already home to four of the world’s longest floating bridges. However, the light rail bridge will need to be 30 percent heavier than what the bridges are currently designed to withstand.
The existing 1-90 bridge is supported by 24 large pontoons which are watertight concrete blocks filled with air. Buoyancy helps these structure stay afloat and the Times reports that some of the gravel within the pontoons will be removed to prevent the rail cars from throwing off the balance in order to keep the buoyancy.
Another challenge that engineers will have to face are the hinges that join the floating and fixed sections of the bridge together. Below the deck, pontoons are linked together and steel cables anchor them to the lake bed in order to keep them secure even amidst the strong winds and waves.
Another first for Sound Transit:
From 2019 Sound Transit’s Link light rail trains will be run on 100 percent clean energy. This is part of an innovative ten-year agreement with Puget Sound Energy (PSE) and is the first of its kind in Washington state to enable Sound Transit to purchase wind energy directly from PSE's Green Direct programme.
"Sound Transit continues to demonstrate that being a sustainability leader can be done both with minimal expense and maximum positive impact on our economy," said Dave Somers, Sound Transit Board Chair and Snohomish County Executive. "This agreement allows us to make Link light rail service carbon neutral while improving regional air quality and investing in local clean energy projects."
"This innovative agreement with Puget Sound Energy ( @PSETalk ) sets Sound Transit as a leader in providing clean energy services," said Sound Transit CEO Peter Rogoff. "By operating Link light rail on green power starting in 2019, Sound Transit will offer transit users a carbon-neutral option for leaving their cars behind and help reduce the region's greenhouse gas emissions."
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