In my personal (and possibly wrong) opinion, even a very popular train station shouldn’t have enough people to oversubscribe the LTE airwaves and cause signal congestion.
The Atlanta airport has 3x to 4x as many passengers per year as Glasgow central station, and I’ve never had trouble getting good, solid cellular connection when I’m there... so I don’t think the number of people in close proximity is causing oversubscription of the airwaves.
The carrier you use probably hasn’t put up enough towers, or the towers just don’t have enough backhaul bandwidth to do anything useful.
