To make Eastside-only East Link work, excellent transfers are needed

Potential transfer point at the 77th Ave SE drop-off lane (photo by author)

Now that it's much more certain that the entirety of the 2-Line will not open in 2023, Sound Transit has an excellent opportunity to consider still starting Eastside-only service on time: a proposal first publicly voiced by King County Council Chair Claudia Balducci and endorsed by transit geeks across the region.

It's easy enough to demand that Sound Transit only run trains between Mercer Island and Redmond, but putting it into practice is another thing entirely. I don't know if ST staff have backup maintenance and operating plans for this exact scenario, but there are very crucial operational considerations that need to be made, particularly for transfers.

The most obvious gap that results from an Eastside-only 2-Line is the lack of direct service between the Eastside and Seattle. In a world where this proposal actually gets implemented, I expect bus service hours will likely remain along the I-90 corridor between Seattle, Eastgate, and Issaquah. But what about Seattle-bound 2-Line riders (and vice versa)?

The winning option in my mind is a truncated 550 that runs between downtown Seattle and Mercer Island, operating at minimum the same frequency as the 2-Line. Given the capacity differential between Link trains and articulated buses, I would even argue for more frequent 550 service, with two potential options:

• Scheduled service at least half the Link headways (e.g., 5-min 550 service vs. 10-min Link service)
• A load-and-go-style operation where a queue of 550s each take as many passengers as possible before departing westbound

Sound Transit and Metro typically do not operate load-and-go services, so there are intricacies on the scheduling and labor front that would need to be addressed. This option, however, would minimize transfer time for cross-lake passengers.

Accommodating either option would mean optimizing the transfer point on the west side of the station (for departing westbound buses and arriving eastbound buses). This transfer point has not been considered because the bus-rail interchange discussion has focused exclusively on connecting service to and from the east. But given the recent proposal for Eastside-only 2-Line service, Sound Transit would necessarily have to consider a west transfer point on 77th Ave SE.

550 routing in blue; transfer point and west station entrance in red

Although there are no infrastructural accommodations for a bus-rail interchange on 77th, a turnout for a northbound passenger drop-off lane has already been built right outside the station's west entrance. Depending on the paving work, it would be prudent to investigate if this lane can temporarily be used as a bus pick-up / drop-off point until full 2-Line service opens. The big elephant in the room is that this would necessitate buy-in from the jurisdiction in which this all takes place: Mercer Island. Unfortunately, past tensions over this same issue might mean that this idea is a complete non-starter.

Another technical drawback is that the passenger drop-off lane is only about 170 feet long, which is insufficient to accommodate both a potential queue of load-and-go articulated buses and layover space. This might mean a single-end layover point in Seattle, which might end up ruffling feathers on the other side of the lake.

Either way, tradeoffs will need to be made. But if Sound Transit does seriously consider Balducci's proposal, they should also seriously consider making the bus-rail transfers as awesome as possible.