This is an ongoing glitch with Cathcart Circle's PIS. Please fix this bug. It was also a bug in TSW2. This is a screenshot at Pollokshaws East station
I've observed the exact same thing a few times in the BCC route at certain stations (mostly University), but only in poor weather (e.g. heavy rain, lightning storm), and only when approaching the station from a certain direction (in this case it's up from Redditch/Bromsgrove; the glitch never seems to appear when driving into the station down from New Street). I don't get this when spawning directly at the station, even in poor weather conditions. Note that I have been experimenting a bit with engine.ini settings to improve visuals and performance, and I also have some mods installed for this route. I don't know whether it's the settings or the mods that might be causing this, but I'm too lazy to find out because it would take a lot of effort to nail down the exact cause (seeing as I have to drive into the station to make the glitch appear). But if you're not running any mods and have not modified your engine.ini, this is likely a glitch present in the stock game.