So usually a route is given in a set era. We have seen modern day routes and even 1980 routes. But imagine a route where it has 3 different eras. Imagine a new route came out but instead of it focusing on one time frame it could have multiple.This would work especially well with some UK routes as many routes have changed loads since the days of steam and the Beeching cuts. Below is an example of what this could look like. I have done the example based of the current GWR route.
Exactly the idea that i have been attempting to suggest. My threads about GWE branch lines between Paddington and Reading revolve around a similar concept as some no longer exsist following Beeching's cuts.