I’m driving the 12.14 Victoria to Brighton. This is the second time I’ve tried this particular scenario. Each time I’ve been stopped at a red signal just past Thornton Heath. There are trains stopped at red signals ahead and behind. Is this a glitch or is it part of the game?
Depends how long you're waiting for. Some services do lock out. There's a thread here to report them https://forums.dovetailgames.com/threads/london-brighton-timetable-feedback-request.46530/
But in other cases it my be a normal holdup. That’s a busy route and tou will encounter reds from time to time, often with a substantial wait. Check your schedule and see if arrival at your next station seems to allow an abnormally long time
