I have several difficulty when optimizing a smoothed spacing I saw the tutorial here:https://forum.simutrans.com/index.php/topic,9241.0.html
in the line either there will be 2 cases if I set the spacing too low the convoys will boggle up in other words, one lead convoy will end up being overcrowded while the following ones will be almost empty
underspacing.png
on the other hand setting spacing too high will have a similar effect, the convoy will have completed their journey long before the next one departs resulting in several convoys waiting at a station and consequently a reduced service and more overcrowding both convoys and wasted station space.
overspacing.png
there should be a way to calculate the optimal convoy spacing using the timing data that we get from the tab. (ex: adding all the average time together divided by the number of convoys) but adding all the time is difficult and this does not account for mixed speed convoys (fast and slow, freight convoy interference etc...)
That tutorial is outdated. Now you set convoy spacing by ticking the "Wait for time" box.