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In a previous post about Ballard to UW light rail, I wrote a section called “Mixing Lines”. After reading that section again, I realized it is misleading. New information has also been revealed, which has lead me to write this piece, which can replace that section:

Connecting with North Link

There are several ways that the Ballard-UW line could connect with North Link. One of the easiest would be to interline before the U-District station. The only drawback to that approach is that it could interfere with the frequency of North Link, where frequency will peak at four minutes (at least initially).

It would also be fairly simple to require a transfer. Similar systems exist throughout the world, and ask people to spend only a few seconds getting from one platform to the next. We could do the same. The Ballard-UW line could easily be timed to minimize the time spent waiting for a transfer. This would be most valuable later in the day, when frequency on North Link is reduced.

An ideal, but more expensive solution would be to build a spur junction, which provides the most flexibility. The Ballard-UW line would not interfere with North Link during peak hours, but mix the rest of the day. This means that when North Link is running at six minute frequency (or more) a train coming from Ballard would just keep going to downtown. This would enable greater frequency in our core (UW to downtown) while removing the need for a transfer for part of the day. Three minute frequency is well within the headway limits of our system. Building such a junction gives Sound Transit the most flexibility when it comes to determining which trains go where (and how often). I would prefer this option, but it is the most involved and the most expensive.

North Link Capacity

There is the remote possibility that things could get crowded on North Link. Given the latest information from Sound Transit, it is extremely unlikely that we would reach capacity. But if we wanted to reduce the number of people traveling from the UW to downtown via UW Link, we could always build something like the WSTT. I think the WSTT adds value to the entire network so I don’t want to imply that fears about crowding justify its construction. But the WSTT, which compliments this quite well, is just one of the many ways that we can deal with an overcrowding scenario that is unlikely.