As the picture shows, I have set up an experiment with 4 cities. The main transport is monorail, which is modded to speed 12500, equal to 500kph in real world (magnet leviation train lol) I first build City A, then B, C and D, then back to C and B to set up the correct path. After this, just play A and D and the cities keep growing strongly (I didn't take enough screenshot. The final population is more than 50k and demand is very high)
Now here is the screenshot.