1 Line trains are back on track, and back at full speed, after the successful replacement of worn-out rails between Pioneer Square and Chinatown/International District stations.
This stretch of rail is one of the trickiest in the entire system, featuring both a large curve and steep grade change as trains dive down underneath Pioneer Square.
Another complicating factor for work in any part of the original Downtown Seattle Transit Tunnel (DSTT) is that the tracks are embedded in the concrete. At floor level, things look relatively straightforward – but underneath the roadbed is an intricate network of supporting infrastructure essential to safe train operations.
Replacing the rails also means replacing everything under the rails – and ensuring everything is not just in working order but is improved for the future. In the case of this project, that means improving on our original design for insulating the rails that may also speed up future replacement projects.
First, crews from King County Metro Rail’s track division excavated not just the rail itself but a significant portion of the area around and underneath it. The original DSTT rails are encased in a rubber boot that insulates the concrete around them from corrosion caused by electricity passing through the train from the overhead power system. It is also held in place by fasteners that extend out several inches in both directions from the rail itself – which are themselves buried in the concrete of the tunnel floor.
After excavation and removal, new rails are put into place – and then the sparks start flying. The new and existing rails are wrapped in a mold and welded together using a thermite charge. The thermite melts away everything but the pure metal of the rails themselves, creating a smooth and ultimately unnoticeable connection between the old and new sections of track.
Even after the rails have been replaced and welded together, plenty of work remains. Fasteners must be placed along the sides of the rail to ensure that the tracks stay the exact same width apart – and the height of the rails must also be carefully situated before they can be re-embedded.
This time, however, the rails aren’t embedded in concrete – and they aren’t wrapped in a rubber boot, either. Instead, crews applied a quick setting, fully insulating epoxy mixture into the trough cut out during the rail removal. This work must happen quickly – the epoxy is hard enough to walk on in 15 minutes and fully set in under an hour – but it comes with several advantages.
The epoxy sets much more quickly than concrete – which shortens the amount of time needed to complete the rail replacement – and provides slightly more give than a concrete floor, which will make the ride smoother in the impacted area. Epoxy embedded rails are also more easily replaced, which will make future rail replacements easier and less disruptive.
Most importantly, this rail replacement project could not have been as successful without you – our riders. We deeply appreciate your patience as we performed this necessary maintenance as we prepare for our larger and more frequent future light rail network.