Sound Transit Completes Longest Bridge in Light Rail System
Written by Jennifer McLawhorn, Managing Editor
Sound Transit
SEATTLE - Sound Transit has completed the longest bridge in light rail work. In the Federal Way and Kent neighborhoods, Sound Transit could begin testing its system integration by the end of 2024.
Trains are expected to travel along the 7.8-mile segment between Federal Way and SeaTac in 2026. However, crews have completed a bridge structure that runs parallel to I-5 near South 259th Place in Kent, according to the Kent Reporter, and testing may begin soon. Previous alternatives for this route ran along Pacific Highway in order to avoid the unstable soil of the wetlands.
Structure C, as it’s called, is “the longest span bridge in the entire light rail system at 500 feet.” Federal Way Mayor Jim Ferrell expressed his feelings toward the “impressive” structure and how Ferrell believes “it’s going to really expand the footprint of Federal Way.” As for the specific I-5 route, Ferrell said “Number one, we have put in $120 million of improvements into Pacific Highway over the course of 18 years, so the last thing we wanted to do was have light rail come in and disrupt and destroy all that infrastructure. . . we felt it would bisect our town. As Sound Transit went with the I-5 route, it was important to remember that “this is hundred-year infrastructure,” according to Mayor Ferrell.
A challenge crews ran into included requiring the use of divers. According to Sound Transit, “in one of the shafts, a rebar cage that is meant to slide up the poured concrete pillar as it is poured got stuck. The hole that the pillar was meant to be poured into was full of water because the water table in that area is so high, so to extract the stuck rebar cage, they had to send divers down into the water.” These divers worked on the cage by touch because visibility was non-existent due to the mix of water, soil, and lubricant. This was just one such challenge crews faced during construction.
Sound Transit had to anticipate other future challenges, such as the steel rails that the trains run on that contract and expand due to changes in temperature. To address and reduce the likelihood of this, a sliding rail expansion joint was added to allow rail flexibility. With the bridge construction complete, crews will begin working on other areas of the system.
