In my 16 years of Trainzing experience, I will say this. Long routes are wonderful if you have the patience to get them working, but there are some things to consider here. The shear length of the route makes the drive boring. Yes. Unlike the real world where there are things to watch out for, on our routes we have the same scenery each time we drive the same route. I have found that once I get into the slog of the long drive, I find myself dozing off.
AI drivers become stupider the longer the route is. Due to the larger memory load, the AI data stream tends to get bogged down. As time goes on, the AI will start forgetting their routes, skipping signals, junctions, take sidings instead of mainlines, etc. You can troubleshoot this until you turn blue in the face and red in the ears to no avail. Resetting a parameter, or setting up a signal here and there will seem to work, but it doesn't last and soon enough the AI will get dumb again.
Setting up a driving session, not just driving your own train, can take days or weeks and this doesn't count the troubleshooting afterwards. While we have nice tools such as Schedule Library which makes things easier, it's still a long haul no matter how you try to break it up. On a mega merger I put together, it took me about 2 weeks to get the schedule setup not counting configuring ATLS crossings, and then the subsequent troubleshooting which is inevitable with a route session. A route this big needs tons and tons of portals, and both active and static consists. Setting these up, along with configuring the commodities and industries is a task in its self. Then there's a program change, a crash, or some other stupid event, and everything has to be done over again.
A route that size becomes a slog to build. Seriously. Merging is one thing, but building from scratch becomes a bear and a huge one at that. A smaller route, let's say just under 100 Km (64 miles), can take years to build. You see it's not just laying tracks down that makes a route. In fact that's really the easiest part of the task. The other stuff, the stuff that makes the route what it is, takes the longest. Finding that perfect building for the spot, populating a forest, looking for the right bridge for a particular location, and so on. If this is a prototypical route, based off of actual terrain, this is an even bigger matter. With a prototype you're then search for, relying on the goodwill of others, or creating the specialized assets yourself. This alone can mean years of making parts, and that can become a subset of the hobby its self.
The terrain size can become an issue. The largest route can be is as big as your computer can handle, but the largest route as said above, is the sum of all the parts. The number of baseboards is part of it, but a higher resolution terrain, at the 5 meter grid and not the 10 meter grid, can increase your data point size, making the ground (.gnd) file larger. You see the route exists as a sum of many files in a folder so when we see the actual route size in megabytes, it's the sum of all these other files packaged up. In addition to the ground file, there is a objects file, and others including a track file. The objects file contains a small database of all the objects placed on the route. This file can be many 10s of megabytes as a route grows. I have some routes that contain 14,000 assets including trees, buildings, and other assets. The track profile information including the track-type and configurations is tracked in the .trk file. This too can become quite large. The problem is all this data needs to be loaded up when the route is opened up in Surveyor or Driver. This can take time, and as mentioned, the larger the route the slower things will run as well due to the amount of data being handled.
I'm not saying this to discourage you, and by all means do this if you wish, but in the end is it really worth it making such a large world? Ideally yes it would be great to load up a highly detailed, superbly done route of 100s of miles or kilometers, but in the end it's just not worth it. To be honest, I have more fun driving my 7.5 mile, plus a couple of branches terminal and switching regional tram and freight route than I do slogging on the miles of my larger routes which always ends up with an issue with the AI drivers somewhere along the way, making the driving session into a frustrating and dreadful experience.
