You could try my Morristown & Erie, modeled after the prototype, about 10 miles long, or my Eastern Shore Railroad set in the Delmarva peninsula, also a prototype road.
The short line mentioned by George, above, is one of the best available. In fact, any route by George is an absolute work of art. All are highly recommended, though you might find them somewhat demanding on your PC.
If you find that your 'puter struggles with George's routes, you might like to consider the routes that I have on the Download Station. They are not as detailed as those by George but provide good frame rates on mid-range PCs and all the dependencies are on the Download Station. Search under "philskene". Sessions are also available for most of the routes, for example see here:
What are you looking for in a shortline? Lot's of local traffic? Good scenery? My railroad, which is classified as a shortline, has 103 miles of mainline track. Lars has a well detailed Santa Maria Valley Railroad GAURC - Index with about 15 miles of mainline track. Are you looking for a model layout type route or a prototype route the goes point to point and not round and round the train table? Or do you consider a shortline a one square layout with 8 industries and less than a mile of mailine track? Do you want a rural grainger route or a heavy industrial route? There are so many choices . .
Look at all the routes by George and Phil. Phil is being a bit modest as both these guys produce really great good looking routes that run very well. I've spent many happy hours running their routes
Cheers
PJ
I would like to ask what version of Trainz you have, as I would imagine many of George's layouts are TRS2006 SP1 based, but, if you have that then I personally suggest getting his Morris & Sussex layout from the DLS, only 10 miles long, but, absolutely superbly detailed, it does have his super high poly track on it, but, you can exchange it if you like....If you only have TRS2004, then any of Phil Skene's are heartily recommended.
These guys are just way to modest, let's all bang the gong for Phil and George.....:hehe: