Signalling and train control systems

Can anyone suggest a source for information to understand both FRA and FTA passenger rail operations?
I am trying to find out about the hardware and software equipment compatibilities and differences. I am part of a group recommending extending a rapid transit line to replace a CR line, so costing it out requires some idea of what can be reused(if anything) and what needs replacing.

Good luck. A number of large consulting firms make boatloads of money doing exactly that kind of work. You’re unlikely to find someone actually qualified to do it, who would do it on an ad hoc basis.

Jim