Those creations with the red, blue and black lines on default grey terrain were built with the MicroDEM/HOG/TIGER approach, most of them in the early days of Trainz, before TransDEM was around. With HOG, all geo data processing was left to MicroDEM. HOG concentrated on converting plain bitmap images to a Trainz ground file structure. The only suitable map that MicroDEM could combine with DEM data was the US census TIGER data set which happened to be a vector map and MicroDEM happened to have a renderer for this that produced the very colours you see in the HOG-generated routes.
The disadvantage was that TIGER scale is only 1:160,000, a bit on the low side. It may not have been that important 10 years ago because the DEMs weren't very detailed either, partly due to the heavy smoothing applied by HOG to prevent terracing. Nevertheless, you will still be able to find several places in those route templates where rivers are flowing uphill.
I thought about providing direct support for TIGER at a time but abandoned that idea soon after because of the low accuracy of the TIGER vectors. Imagine that your excellent 1/3 or 1/9 arc sec NED DEM shapes the earthworks, your cuttings and embankments/high fills, and the railroad track is placed hundreds of feet off, running straight over the hill crest. It wouldn't be that much fun.
Generally, vector data processed by TransDEM will end up as Trainz splines. Good vector data for the US can be downloaded from the Open Street Map database but needs conversion to become compatible with TransDEM. I recommend JOSM for this purpose, see
Open Street Map Vector Data in TransDEM with JOSM.