I recently posted a new idea for full-line route development, but I was a bit sloppy when presenting it, so I want to present my expanded version of this idea. But first I want to say that I support more extended and merged routes than this, but we have to think what is actually possible to make true. And making a full line route from start to end in one part will take more time, and time is money. So let's get started. Full-line routes can be developed and sold in smaller routes, which all has same timetable. When completing a service in service mode, there would be a new button in the debrief menu, "Continue service". When pressing this button, it will auto-load you into the same station in the next part of the line with same rolling stock and weather presets. When completing a scenario, there would be also a new button in the debrief menu, "Continue scenario". When pressing this button, it will auto-load you in to the next route, and the next scenario what you will drive is a sequel for the previous one.
