It's a glitch then. There's a few services in the game that are like that. Sorry I couldn't be of more help
Have you coupled up trains / waggons that might not be intented to be coupled? As that can lead to red signals aswell.
Depots? As in yards etc? Are the lights red because they’re just not part of the drivable route yet until the NTP freight pack arrives?
Am I right in thinking that you have spawned on foot in the depot and randomly want to take a train for a drive? If so, service mode does not allow you to drive anything other than scheduled services running on their timetable. So, if a train is due to leave, the lights will go green, if you are outside of any scheduled service, they will all be red. *I wish it did allow us to do this, however we could not have a running network with AI traffic if it allowed you to just hop in and drive anything at any time. I would rather have a realistic route with AI traffic on a realistic timetable than 'free drive'
You couldn't just hop in and drive one out and onto the mainline. You would encounter a red signal too
You can have fun in Thornaby Depot with the Gronk, I like shunting a 37 between depot lanes. You still get red signals in the depot, but two or three Gronks spawn, along with one or two 101s and several 37s. If you get creative with the shunting there is plenty of time to kill in there!