Comments on: Sound Transit Tests Link and Buses Sharing Tunnel

By: Oran

Oran — Tue, 01 Jul 2008 02:02:56 +0000

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.

By: Buzz

Buzz — Sun, 29 Jun 2008 22:17:29 +0000

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.

By: Gordon Werner

Gordon Werner — Sun, 29 Jun 2008 15:36:04 +0000

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

By: Ben Schiendelman

Ben Schiendelman — Sun, 29 Jun 2008 06:42:23 +0000

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.

By: Roger P.

Roger P. — Sun, 29 Jun 2008 05:43:01 +0000

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.

By: Gordon Werner

Gordon Werner — Sat, 28 Jun 2008 19:55:27 +0000

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

By: AJ

AJ — Sat, 28 Jun 2008 19:27:54 +0000

Like Interstate MAX.

By: Ben Schiendelman

Ben Schiendelman — Sat, 28 Jun 2008 15:57:05 +0000

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.

By: Christo

Christo — Sat, 28 Jun 2008 05:55:31 +0000

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.