I made my own system that works for me. It is as follows.
Intercity = IC-B-City name-# for instance it would read. IC-B-HAR-1 That tells me it is intercity bus route 1 for Harwood. I also use trams, that would read, IC-T-HAR-1. For city city I would use.. CC-TR-HAR-DOV-1 That would mean, City-City Train route 1 for Harwood to Dover. FRT-R-G-HAR would mean Freight Resource, goods going to Harwood. FRT-R-O-1 would be Freight Resource Oil route 1. Just find something that means something for you.
It works for me. As to the replacing issue, I solved it by having each of the vehicles being replaced every 5 years. So, 1900 I replace all bus’s, 1905 all trams, 1910 all trains. Every vehicle of that type gets replaced at the same time, saves time and headaches. Note: I always replace any line when a new vehicle is on line. 🙂