Seattle’s Sound Transit is investigating the cause of cracks in the rails of its signature Link light-rail system.  Discovered as part of a routine inspection in mid-September and since repaired, the cracks occurred along a 1,200-ft section of the line’s northbound crossing of Interstate 5. Although the damaged rails were deemed safe, Sound Transit trains operated at substantially reduced speeds through the affected area until the entire five-mile section, opened in late 2009, could be fully assessed.

No other track irregularities were found, says Sound Transit spokesperson Kimberly Reason, who declined to estimate how long it will take to diagnose the cause of the cracks.

“We have qualified maintenance staff performing this effort,” Reason says. “Testing of subject rail will be performed by independent laboratories.”

The area where the cracks occurred is part of a nearly five-mile segment of elevated guideway between South Seattle and Tukwila. PCL Civil Constructors, the general contractor for the segment, has not been notified of any issues with the work, according to a company spokeswoman. RailWorks, the subcontractor responsible for the guideway tracks, did not respond to a request for comment.

According to a 2007 announcement from Sound Transit, nearly 85% of the Tukwila section’s trackway is elevated, supported by 190 columns up to 70 ft in height. More than 2,450 precast concrete segments were placed using a 385-ft-long gantry truss system relocated from one column to the next as spans were completed. The Interstate 5 crossing was built using a balanced cantilever approach, the statement said.

Now stretching nearly 20.3 miles from the University of Washington to south of Seattle-Tacoma International Airport, Sound Transit’s light-rail line carried more than 23 million passengers in 2017. Several expansion projects are underway, including a four-mile northern extension currently scheduled for completion in 2021. The agency plans to build out the 116-mile light-rail network by 2041.