I'm curious as to why nobody has ever made a combination of the two, something like you get started on some large map with prebuilt cities and terrain and you have to build lines to different industries, hauling them for money. you can't build track or buy engines without money. And, once you've got a line built, you can take one of the engines out and go pick up what's needed and take it to it's destination earning you a sum.
You almost exactly described one of my all-time favorite games.
It's called Chris Sawyer's Locomotion. It's based off of one of the first Roller Coaster Tycoon games and is from 2003/4 with DirectX 9.0b graphics. I personally get addicted to it every once in a while since it is so simple, yet vast in scale and depth with hundreds of add-on vehicles from sites like
AMI Trains. The timeframe starts at 1900 with vehicles from the era and goes forever, with new vehicles coming and going every 15-25 years or so. I highly recommend it for people looking for a basic and fun game to play.
There are built-in scenario and map editors that are pretty basic yet you have full control of the terrain and objects. One thing though, is that everything is based on a grid system (more than Trainz) where everything must be built one grid at a time. The grids are decent in size (enough to fit a house on it), but when building long distances, they can be a pain. The maps are non-adjustable in size, but are pretty big in the first place so you will almost never run out of room.
The economic side is a little less complicated than the Railroad Tycoon series in that there are just a few things: Loans when you need it (like when first starting the game), infinite money (as long as your company makes money, you'll keep getting that money), and you rise the corporal ladder (from Platelayer to Engineer all the way up to President and then Tycoon). I could go really in depth into Locomotion, but it's better if you go and find out for yourself.
It is a very fun and addictive game that is an awesome time-passer. Highly recommended.
My thoughts.
Kyle