The Epoch system introduced in A-Train PC Classic affects your transport company and the decisions you can make based on the current year. In the middle of the 20th century the types of trains and tracks available will be limited. As time passes you can either research new technologies or take advantage of others' research to replace your obsolete rolling stock with better and newer trains, stock resources underground, and much more.
Sometimes it's a balancing act -- should you make a costly upgrade and save money over time, or stick with your existing technology for a few years? It's these choices and the ever-changing environment of the game that makes A-Train PC Classic such an interesting game to play over and over again.
Scenarios are set in various eras, from the 1960s to today, and mastering the technology available to you in each time period will often be the key to success.