How much ram have you got? I was successful merging the routes with 32GB of ram anything lower than that I was struggling with lag and performance
and sometimes the game didn't respond, so I upgraded my ram
In surveyor, load up the Illawarra route use the mini map and load all baseboards it helps cache everything. Same rule applies if you merge the other route, you need to load the baseboards in the map views
In that thread, I did mention it to the other lad to use the mini map and merge map window to load the baseboards.
Rand, Kywong and Holbrook branches all connect to the ARTC NSW Main South - VR North-East route as shown in the above map
Grazlash has used his ARTC NSW Main South - VR North-East v2 route