Both transit advocates and politicians have been discussing the idea of a second downtown transit tunnel through Seattle, which would act as the foundation for future rail service to Ballard and West Seattle. Seattle Subway’s proposal currently looks like this and seeks to address a few issues:
- Mitigates the closing (for buses) of the current Downtown Seattle Transit Tunnel by building the tunnel initially for buses
- Provides capacity enhancements in the downtown core
- Can provide exclusive lanes for buses heading to West Seattle and Ballard
The proposed tunnel could also have a few drawbacks:
- Costs of unused railway infrastructure: If the tunnel were to be built initially with railway infrastructure (tracks, power and communications) as Seattle Subway suggests, these would still require some form of maintenance even if they were not being used. These infrastructure components don’t stand still over time, and will have an aging effect. No one really knows how long it would take for rail services to begin, but it would be a waste to maintain infrastructure that is not being used.
- There are only 3 stations (Westlake, Madison and International District), fewer than the current DSTT. Although this would give a direct connection to Madison BRT, it would also mean that buses serving the new tunnel have farther stop spacing and potentially shorter travel times than light rail in the DSTT, the opposite of what it should be.
- Conversion to rail could be a slow process due to institutional and political inertia, which may result in another DSTT situation where buses are “phased out”. The lesson to be learned from the DSTT, is that joint-operations is difficult and results in unreliable service for every mode, even six years into operations.
- Alignment constraint in the current DSTT are not addressed, such as the Westlake or Chinatown curves
In an attempt to explore how these issues could be resolved, I’ve created another proposal, which is a tunnel on 4th Ave that will accommodate all light rail services from the beginning and in the future. The current DSTT will then serve buses (again) and potentially streetcars. The “Westlake curve” will also be removed, allowing higher speeds in the tunnel. I’ve listed a few key advantages of this proposal.