I tried this as well. On a large map I connected every single town to every single town in a giant wheel (I had a few billion) and they would eventually end up in a cluster of trains with the main one picking up passengers and the other ones lagging behind it. I started using one way lights to space them out individually so no single train could be on a track between cities. A single one way light placed at the end of every platform helped me control that to some degree. Keep in mind this is a one way ring.
Trams don’t seem to have this problem as there is simulated traffic that allows them to spread out.