When we talk about building West Seattle or Ballard service, there’s often an assumption that this service could use the Downtown Seattle Transit Tunnel we have now. As far as I’m aware, it can’t.
The light rail spine we’re building now will eventually go through Federal Way to Tacoma, and through Lynnwood to Everett. The tunnel will be used not only for trains that run straight through from Everett to Tacoma, but also for trains that run from Everett (or at least somewhere north of downtown Seattle) to Bellevue and Redmond.
We’re starting with service on Central Link every six minutes during peak times. It’s probably reasonable to consider service down to headways (time between trains) of two minutes – the closest headways I’ve seen in any Sound Transit documentation are 2.4 minute, from their 2005 long range plan.
After University Link opens, I sincerely hope we’ll be looking at lowering headways during peak times. Maybe this will be to five minutes. If we build Sound Transit 2 just to Northgate and Bellevue, we’re going to add trains to the tunnel to bring headways down further. We’d have trains to the Rainier Valley every five minutes, and then trains to Bellevue every 10 minutes. The easy way to figure out combined headway is to figure out how many trains that is per hour – 6 for Bellevue, 12 for the Valley – and then divide the number of minutes (60 in an hour) by the number of trains (18). Let’s round this to 3 minutes.
This is a hundred year plus system – it’ll still be operating after all of us are long dead. We’re certainly going to increase the frequency of the trains on this line in the future – maybe even soon. We need the flexibility to do that.
Ten years ago, the monorail project was talking about 3 minute peak headways for Ballard-West Seattle. Combine that with just the potential ST2 service, and you’re talking about 1.5 minute peak headways. Those are physically possible, but that’s it, then. We wouldn’t have any room for ST3, no room for ST4, nothing.
New rail through downtown will need new right of way.