As part of ST3, Sound Transit is planning to run three BRT lines (branded as Stride), two of which will run predominantly on I-405. These are going to be line S1, running from Burien to Bellevue, and line S2, running Lynnwood to Bellevue. Both lines are going to meet at Bellevue Transit Center, where transfers can be made from one Stride line to the other, or to Link or other bus service. Details are vague; Sound Transit has only said that the Stride S1 and S2 lines will serve the existing transit center, but has not said which bus bays Stride will serve. Sound Transit has also not said where buses will layover after arriving in Bellevue, and whether there will be additional BRT stops at the layover points.
Currently, ST Express routes 560 and 535 (which will be replaced by Stride when it opens) stop at Bellevue Transit Center immediately after exiting the freeway. But both routes continue beyond the transit center to their respective layover locations, and in both cases, there is a bus stop there (the 535 also serves multiple bus stops near Bellevue Square on the way to its layover stop). When Stride opens, both routes (which run every 30 minutes at best) will be replaced with much more service, with headways at 10 minutes during peak and 15 minutes off-peak. This fact is significant because it will further squeeze the peak capacity of Bellevue Transit center.
Buses moving westbound within Bellevue TC typically move reasonably smoothly. However, eastbound traffic has a tendency to get jammed. In my experience, aside from the magnitude of outbound peak service, this mostly caused by routes 566 and 567. Pre-COVID at least, route 566 operated with 10-20 minutes between buses, and route 567 operated with around 20 minutes between buses (to line up with Sounder service in Kent). In the afternoon, both routes hit a major choke point at the westbound SR 520 to southbound I-405 ramp. Traffic here gets so bad that travel times in the afternoon from Overlake TC to Bellevue TC are scheduled to be as much as 25 minutes, a large buffer to ensure reliability for service departing Bellevue. However, actual travel times are very volatile. It was fairly common both to see buses arriving in Bellevue 10 minutes late, as well as 10 minutes (or more) early. This means that every so often, you would see a 566, a second 566, and a 567 all arriving at bay 6, and the one in front waiting until its scheduled departure. Since the bay cannot hold all three, every bus behind it (which includes 3 routes with 10+ minute frequent service, among others) are all stuck waiting for the bus in front. This frustrating situation has the potential to get even worse when Stride comes in with a net increase in bus service.
Furthermore, per a draft SIP Sound Transit released in 2018, the agency plans on continuing to operate routes 532, 566, and 567 (the first two being modified to serve stops that would be left behind by converting routes 535 and 560 over to Stride) during peak, despite this service being significantly redundant with Stride. This was before Sound Transit starting evolving its options for Woodinville, which include another bus to Bellevue during peak. This means that afternoon capacity issues at Bellevue TC are likely to be worsened by Stride if bus bay assignments are not carefully considered.
The most significant change would be to move the B-Line over to the other side (reversing the direction of the loop through Bellevue TC), which would move the layover from the eastbound platform to the westbound platform. This would help matters because eastbound bus bays could be spaced further apart. But at the same time, westbound capacity would be squeezed, as there would be more bus service and bus bays would have to be spaced closer together to accommodate layover space for the B-Line. Route 250, along with its own layover, might have to be bumped over to the eastbound side, which would undo some (but not all, due the smaller coaches used on the 250) of the capacity gains of moving the B.
A better way might be to solve this problem might be to move the Stride station outside of the main transit center itself, and into new bus bays on 110th Ave NE, in between the existing transit center and Link Light Rail’s Bellevue Downtown Station:
Doing this would free up a ton of capacity inside the Bellevue Transit Center, while maintaining a good overall rider experience. While a bit less convenient for bus transfers, this arrangement would be more convenient for Link transfers, as riders would not have to cross the street when switching from Link to Stride, and the reverse crossing would still require minimal walking to reach the train. The drawback with this approach is that it reduces the flexibility in placing the layover space. This would work reasonably well if Sound Transit has Stride buses layover at the current 560 layover area by Safeway, but using the current 535 layover space by the mall would not work very well with these station locations.
Another possible configuration is to combine the presumed placement of stations inside the transit center with the 110th Ave NE concept, by placing the inbound station at Bellevue Transit Center (most likely at bay 7 or bay 8, and possibly both depending on the line), and the outbound station on 110th Ave NE, at the front door of Bellevue Downtown Station. This, in many ways, is the best of both worlds. Keeping the inbound station inside Bellevue TC is less of a stretch in terms of capacity than the outbound station. Passengers don’t need to queue for inbound buses (unless there is a layover stop, which would likely see little usage), and inbound buses don’t need to wait before departing, so they will be in and out. The outbound stop would get its own space on 110th Ave to load passengers, where it will not disrupt other Bellevue TC service, and passengers will have plenty of open space in front of the Link station to wait for the bus.
Additionally, this opens up the possibility of having layover space on 110th Ave NE in front of City Hall. Should this be done, then this will allow buses to take the shortest possible loop to get to the start of the next trip, with the layover on the way. Though that space on its own would be unlikely to be sufficient for peak Stride service, it could still augment rather than replace ST’s planned (or TBD) layover capacity. Operators running late could head straight to the City Hall space, while those with time to spare could go to the main layover space. For off-peak service (which will operate every 15 minutes), the space in front of city hall could be sufficient. With traversal of downtown Bellevue streets being slow, having a small loop like this could save enough time to be able to operate with fewer coaches in service at all (or almost all) times, which would be huge.
This concept is not without its challenges. City leaders might not be so happy about having buses waiting in front of City Hall, after Sound Transit tore up their park for Link. 110th Ave NE would also have to be reconfigured to move general traffic away from the curb (which would probably involve reducing southbound traffic to two lanes, and adding a second right turn lane onto eastbound 6th St.). But larger infrastructure changes are not unprecedented at all for Stride, and such a small, cheap change would benefit both lines at the place that will see the most ridership, so it’s reasonable to hope Sound Transit would at least consider it.