The first section of Sound Transit’s East Link rail installation comes with an extra level of ballast. A 7,200-ft-long stretch of track that runs along Interstate 90 on Mercer Island includes a special construction component.

As contractors install rail on concrete ties, they continue to set them in large rocks, or ballast, forming a bed for the tracks. The installation process for the ballasted tracks starts with applying a rubberized material to the existing pavement, known as a “ballast mat” and then applying an even layer of ballast along the ground under the tracks.

Workers then set prefabricated concrete ties evenly set atop the ballast. Once ties are set, crews thread long sections of 960-ft-long steel rail through clips on each end of the ties. To polish off the process, crews flood the rail bed to bring the layer of ballast flush with the top of the ties. A machine rolls along the rails to tamp the ballast and uses a laser to measure the height of the rail and adjust the level of the ties necessary to maintain a consistent height.

As the East Link project extends light rail 14 miles from downtown Seattle to downtown Bellevue and the Overlake area of Redmond via I-90 with 10 stations in time for travelers in 2023. Construction has reached 40% completion on the project. The laying of the ballasted track between the Mercer Island Station and East Mercer Way marks the first section of track built on the project.

In 2019, crews plan to install rail on the Homer M. Hadley floating bridge using an innovative track bridge designed specifically for placing fixed track on a floating bridge to accommodate lake motion and allow light rail vehicles over the floating section of I-90, the second-longest floating bridge in the world behind only the State Route 520 floating bridge just north of I-90.

Sound Transit is simultaneously working to extend light rail north, south, east and west, opening new stations every few years to form a 116-mile regional system by 2041. Starting in 2021, the Northgate project will provide reliable, congestion-free travel to Seattle’s University District, Roosevelt and Northgate neighborhoods. Northgate Link will be followed by the opening of service to Mercer Island, Bellevue and Redmond’s Overlake community in 2023. Additional extensions to Shoreline, Mountlake Terrace, Lynnwood, Kent/Des Moines, Federal Way and downtown Redmond are planned to start service in 2024. Further light rail extensions are scheduled to reach West Seattle, Fife and Tacoma in 2030; Ballard in 2035; Paine Field Industrial Center and Everett in 2036; and South Kirkland and Issaquah in 2041.

Follow Tim Newcomb on Twitter at @tdnewcomb.