The picture @Riverside shared makes the sequence clear, but one of the instances where non-geographically-accurate diagrams can cause confusion. The Congress St. stop is at WTC. They are essentially the same stop twice, but on the line diagram, they're shown two stops apart.
This can be somewhat ameliorated by using the "official" name for the stop (insofar as the automated announcement on the bus is the "official" name):
Congress St at World Trade Center -- or on a map,
Congress St at WTC or
Congress St/WTC.
Actually, why does the Congress St. stop exist? It wouldn't save much time to skip it, but some. And in my experience, it's a pretty quiet stop compared to all the people trying to get to South Station. Does anyone have numbers handy, out of curiosity?
Adding on to the numbers
@TheRatmeister presented, I've always assumed that the stop was included because they wanted to avoid complaints from business travelers going to conferences at the WTC, coming from the airport -- it's been a long trip and it'd be maddening to get stuck on the bus when it's literally driven right by your destination. (Especially if it gets stuck in rush hour traffic.) To your point, it's bad design to have the route go in a loop, but it's also bad rider experience to force riders to go the long way around when it's easy to drop them off.
In that case, will SL1/3 just be able to turn into the bus tunnel from D Street? Either way, this still looks like it'd be reasonable to drop the Congress St. stop. Otherwise, it's effectively doing the same stop twice, mere seconds apart. People who would have alighted at Congress St. could just get off at WTC, adding seconds to their trip. Meanwhile it would (slightly) speed up the trip for what looks like the vast majority of the bus trying to get to South Station.
Hmm, I'm not sure I agree with that calculus. There are three traffic lights between Congress St/WTC and the actual World Trade Center station. I don't know the exact timing of those lights, but
assuming an average cycle of 60-90 seconds, and assuming the bus is held, on average for half that time at each light (30-45 seconds), that's roughly another 2 minutes on the trip. (And sometimes it will be more, if they get really unlucky.) That's obviously not terrible, but I think it's non-trivial.
The entire fact that there isn't a direct connection from the TWT into the Silver Line's tunnel is the real culprit here. Everything else is mitigation of that, and I think at least some mitigation is appropriate.
Here's the hot take: replace SL1 with a pair of Logan Express services, one express to South Station and one to the Seaport. With a bus lane on Congress St that is guaranteed right-on-red, the Seaport route could limit itself to 2 lights (Seaport Lane and Silver Line Way) before getting right back on the highway.
