There's nothing stopping you from fixing the route. The route is extremely well done and with some patience, you'll have something you can drive and enjoy.
What happened is he built the route originally in an early version of TRS19. The initial versions of TRS19, like earlier versions of Trainz, required users to tamp and lock down roads by clicking on the spline points to prevent the roads from floating whereas later versions, just as it is now, allow roads to sit on the surface of the terrain and lay flat without tamping them down with bridges being the exception and required a click on the spline points to prevent bridges from collapsing.
This isn't the only problem. the ground textures are PBR textures and road assets that don't always work well with PBR textures. To fix this, you need to spread out the the textures under the roads by painting a wider area under the roads. or by disabling the 3d-effect of PBR textures. You do this by setting the Shader to "Basic" in the Performance settings.
There are many other things that occurred only to add insult to injury such as the destruction of TRC crossings, thanks to the changes in program code that broke them multiple times requiring reconfiguring them in the session instead of the route and then reconfiguring them again in the route. It also didn't help that he had objects on the wrong layers, including placing trains on the route instead of in a separate session, causing trains to derail due to other trains being buried under the terrain.