I’m seeing the same behaviour omoikane, Yeol, and Mykel Razi observe. Buses and trams work like a charm; as long as you use one type of vehicle on a single line, they will spread out fairly evenly, even when part of the line runs through busy streets shared with other lines. Really nice!
Trains don’t seem to spread out reliably. I’ve had a line connecting three towns (two termini and one station in the middle) with various trains from the 1890s to the year 2000 — but always the same trains at any one period — usually with three trains on the line, but they would invariably bunch up.
The lack of platform selection sometimes caused them to wait for trains from other lines using the same platform, so that may have been an attributing factor as well, but by means of test I have removed all switches from this line except for those before the termini, forcing the whole line on dedicated tracks and platforms, and stopped one train to let the other two catch up to it, then started all three (all TFVs) and let the game run for ten years. They spread out a little, but they still followed each other much too closely.