I would add here that some people get slightly funny about looking for them on Linkedin, so just be careful and mindful that they may not want appreciate or respond the way you may expect.
Ive had people message me on instagram which is a bit too personal. I know it shows initiative yes, but, but to some, it can be percieved a little differently.
I understand peoples frustrations about being in a talent pool, but what this system is designed to do is to be able to pull names out of this pool when vacancies arise. You are not applying for a vacancy that already exists, which means yes, you may actually be in here for a while, and longer than anticipated. I almost advise people to apply and then keep their options open or forget about having applied. The talent pool is a long term game, not a short time push. Some TOCS are better with keeping people in the loop than others, but with changes in personel and business requirements within the rail industry constantly, efficiency can rise or fall accordingly.