Last Friday night, Sound Transit tested Link Light Rail sharing the Downtown Seattle Transit Tunnel with buses.  Buses and Link will share the tunnel until Link headways and/or extensions eventually re-align bus service to the surface.  Here’s how the test is described in this week’s Sound Transit CEO Corner:

Last Friday evening, after the Downtown Seattle Transit Tunnel was closed for the weekend, we successfully ran light rail trains and buses together in the tunnel.

This was a significant achievement — the first time ever that trains and buses ran together in the tunnel. Friday’s test was necessary to make sure the tunnel’s signal system works properly, allowing trains and buses to use the tunnel at the same time. The good news is the test showed that the system works very well and trains and buses can both safely occupy the tunnel.

Two light rail trains and nine buses were used in Friday’s test, which took about 90 minutes.

9 Replies to “Sound Transit Tests Link and Buses Sharing Tunnel”

  1. What exactly will be the relationship of the train to buses? Will it get the right of way? Will it yield to buses? I was wondering about the same issue on MLK. Will Link stop at intersections or will traffic lights be timed around it?

    I’ve not been able to find a place where these questions are answered.

    1. Trains and buses will take turns at each tunnel station. Neither will really have to be in a position “yielding” to each other – a pack of buses will move through, followed by a train, then another pack of buses. Part of the work done in the tunnel was to install a new signaling system to keep them separate. Similar systems already keep trains separated from each other on regular railroads around the world.

      On MLK, lights will be timed for trains in the peak direction, and to the extent possible in the off-peak direction. You shouldn’t stop for lights in the peak direction (or maybe one, I think there are a couple of pedestrian request buttons that might force it), and you’ll stop for a couple in the off-peak. You can’t time it in both directions at the same time, there are too many lights and too many trains.

  2. they should test the LRVs with the public so that we can get a chance to ride the damn things

  3. Small addition to what Ben said. Behind each train entering the tunnel, a platoon of buses will follow. Two minutes before the next train is to arrive, buses will be stopped from entering the tunnel, until the train has passed.

    This gives a two-minute safety window in front of each train, so we don’t have trains coming up behind buses while in the tunnel. The buses and trains are extremely reliable and safe, but if there ever is a failure, we don’t want it to result in a train running into the back of a bus.

    Ben has a good description of how MLK signal lights will operate. The operating computer will be programmed with the train schedule, so it will “know” when each train is coming through, and adjust the signals accordingly, with, as noted, priority for the peak direction. This is much more sophisticated than a typical pre-empt system that simply turns every signal green for the train when one arrives — that would be too disruptive to crosstraffic and turning traffic.

    1. Thanks, Roger! I didn’t know there was such padding in the tunnel – is the two minute window for each station?

      I also didn’t know that the MLK signals were smart – I only knew they were timed, and assumed it was blind timing, preprogrammed. Very cool that they can adjust.

  4. are you sure? it would make much more sense if the system detects where the LRVs are and sets the lights as appropriate … this would avoid problems if the LRVs are delayed due to longer-than-expected station boarding or whatever else might prevent them from moving along on schedule.

    Think railroad crossing gates … they simply detect a train and trigger the gates and lights to activate ahead of the train … all based on speed and direction

    1. I think they would put Transit Signal Priority in the signal controller cabinets that will give or extend green time for trains that are running behind schedule.

  5. What? Buses and trains together in the DSTT? Why, what happened to single mode purity? According to anti-transit pretendgineers at Kemper Development Corp and CETA, the transit world should have ended last Friday. I’m sure Emory Bundy and John Niles are cooking up their next domsday scenario predictions right now.

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