For the next few months, Sound Transit is installing new sound walls in Tukwila around Central Link. The impact on riders is that from April 1st through the end of July, on weeknights trains will drop to 20 minute frequencies after 9pm. Usually it runs every 10 minutes until 10pm and every 15 minutes after that.

I asked ST spokesman Bruce Gray a couple of questions about this:

Are you making any exceptions for game nights?

We’ll be able to have the same number of trains/seats online to clear out games as we’ve ever had. We’re able to clear those post-game crowds pretty quick by having consists ready in the Stadium pocket and ready to roll out of the base. Post-game headways will be more like peak headways because of the extra trains on the line.

We expect big things from the Ms this year and we’re going to make sure their fans have a good experience getting to and from the games on Link.

Why not use the turnaround track at Rainier Beach to maintain headways for most of the line? Between 9 and 10, for instance, it’s pretty straightforward to turn around every other train at RB, maintaining 10 minute headways for most of the line and 20 minutes on the Tukwila segment. Unfortunately, after 10pm the math doesn’t work out so neatly.

Our opps folks call it “operationally inefficient.” It also provides more opportunities for things to go wrong and throw the entire line off schedule… And keep in mind we’re really only talking about an extra 10 min headway between 9-10. After that it’s an extra 5 from the usual schedule.