Ok, here we are: stuck at red at 1.3 miles south of 22nd Street, with 5 (!) AI trains blocked in front of me, and another one stuck at red just outside San Francisco station. Thanks, DTG, another great run ruined by your stupid bugs.
It's an infuriating bug. https://forums.dovetailgames.com/threads/baby-bullet-cab-end-service.21473/#post-129346