-Very powerful trains accelerate fast and then start to decelerate, I assume to keep their distance from the train in front of them, dropping to very low speeds, only to accelerate fully again, instead of keeping a nominal speed. Adding more signals doesn’t really solve this.
There’s currently a bug(?) where occasionally, small (and sometimes very small) segments of track are built that have a much lower speed-limit than the surrounding track. The easiest way to find them is to let a train drive over the segment, and when the last wagon has left, the train will accelerate once again. This is where the slow segment is. The trick is to demolish that segment and possibly a few surrounding segments as well, and then rebuild the track (taking care to make sure those really-small segments are demolished as well). Hopefully, once you rebuild the track, the trains will pass it at a much greater speed.
-When skipping several stations before arriving at the next destination, at the second-to-last station trains slow down for no apparent reason, accelerate again after passing it and then make a normal arrival at the destination station.
Maybe this has something to do with the bug(?) with the small segments – in this case, there could be small slow segments just in front of or behind the tracks of the station.
-Stations should really have exits on both sides, for being usable as a circular line.
Actually, you should be able to use a one-exit station for a circular line, but yes, it would be nice to have stations with two exits, or even better, stations that exit directly into an adjoining bus-station without the people first having to go to the main road and then go to the bus-station.
-When stopping vehicles to clear a road for reconstruction, after removing a road, sometimes the stopped vehicle moves and becomes impossible to select, or even find. The only way to find it again is by sending the entire line to the depot and waiting for the one that remains outside.
In the “All lines” window, for each line, there is a list of all vehicles on a line. If we knew which line the disappeared vehicle was from, we could select all vehicles from within the lines window and open their windows to see which ones are stopped. Of course, it would be nice (hint! hint!) if we could see this list of vehicles from within the window for an individual line, rather than only the window for all lines (I think the list of vehicles should be in both windows).