Many remember Seattle as the setting of the 1993 classic Sleepless in Seattle where Meg Ryan falls for a widowed Tom Hanks. Seattle’s skyline is also easily recognized for its iconic space needle piercing through the sky overhead. The Emerald City, however, is also notorious for its large-scale infrastructure projects that serve to make the city more liveable for its almost four million inhabitants. The newest of these mega projects is a light rail passenger train that, unlike other trains bound to the ground, is going to float more than 200 feet over Lake Washington.

Seattle’s local transit agency, Sound Transit, is planning to build the light rail passenger train on the city’s floating bridge, also known as the I-90 Bridge or the Homer M. Hadley Memorial Bridge. The train is expected to carry up to 50,000 passengers per day at a speed of 55 miles per hour (88.5 kilometers per hour) in two 300-ton trains once the project is completed in 2023. The projected cost for the floating light rail, which was first announced in March, is expected to be about $3.7 billion.

The concept of the floating light rail is not novel to the Emerald City, granted that the city is already home to one of the world’s four longest floating bridges already. The I-90 Bridge, which connects Seattle to Mercy Island, will soon carry the new light rail across Lake Washington, replacing the bridge’s HOV lanes with railway tracks. Unlike other bridges, like a suspended bridge, the floating bridge is not supported by concrete columns or overhead cables. Rather, it will supported by “pontoons,” which are air-filled concrete blocks. The pontoons are linked together and are anchored in the waterbed below, granting the blocks a degree of stability while maintaining the buoyancy needed to keep the bridge afloat. In order to accommodate the new tracks that will run between the bridge’s lanes, the hinges connecting the floating and fixed portions of the bridge will be altered.

Seattle’s experience with eccentric projects to remedy massive infrastructural challenges is not new. Last year, the city completed a “flexible bridge that bends in order to withstand earthquakes. The new light rail system claims that it will reduce the commute time from Seattle to Bellevue from 45 minutes in a car down to 20 minutes. Despite calls by the likes of Judge James Johnson for fostering a “free society” in which people can go where they want whenever they want, citizens of the tri-county area that Sound Transit serves voted in 2008 for increasing a sales tax to expand regional light rail travel.

This is not to say that the planned train does not have its dangers, the worst of which could potentially end catastrophically should the railway tracks collapse. According to CityLab, once the light rail is built, it will make the I-90 floating bridge 30 percent heavier than the weight threshold it was designed to remain under. Withstanding strong winds and water tides also pose a challenge to the light rail project. Although the I-90 bridge sways in the wind, approximated to be two feet in any direction and even possibly tilting with high traffic, motorists barely feel the bridge moving when traveling across it. The light rail, on the other hand, adds to the weight of the bridge, meaning the swaying might increase or possibly be left unchanged altogether. The project plans to incorporate earthquake engineering to adjust the light rail tracks accordingly to ensure the swaying remains minimal.

Seattle’s I-90 bridge and new light rail system are not the only initiatives that the world has seen in an effort to help solve traffic congestion and reduce travel time. In 2016, Norway announced its plan to construct a submerged floating tunnel that runs through inlets surrounded by the country’s idiosyncratic fjord landscapes, which prolong travel time. Similar to Seattle’s I-90 bridge, what is called “Archimedes Bridges” in Norway will be one of the first tunnels of its kind to be constructed, reducing travel time in between fjords from 21 hours to 10.5 hours.

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