Vehicle spacing is there but only for road vehicle lines, so busses, trucks and trams.
To achieve spacing for trains you need to use the stations and signals.
Normally, without any signals, the stations build one area, which trains can reserve for themselves and the tracks in between them build one area each for them.
So to achieve spacing in a line with 2 trains and 2 stations, only 2 signals need to be added:
Station 1 _________________________ Station 2
With this setup, 2 trains should space out automatically, since the first train won’t leave the station, until the
second one has arrived at the second station