Feature request: Trains reserve track by tile, not by segment

[BenLubar]

Right now, trains reserve an entire section of the track and don't un-reserve it until they're out of that section. That means if you have two signals in a station's loop like this, you can end up with both trains stuck waiting for each other:

If you instead only put in one signal, the entire track gets reserved by the first train and the second train can't get anywhere near the station:

If we try to add a signal at the end to close off the second train's section, we end up with this:

My suggestion is that trains should reserve the pieces of track they want to pass through, starting with the first tile the train will enter, and ending with the tile the train wants to move to (either a station or a signal). Then, the train only un-reserves a tile when it passes off of the tile (or to avoid making cosmetic differences in trains have a gameplay effect, keep a queue of the last four tiles the train engine has exited and unreserve the tile that gets kicked out of the queue each time).

This means that in the scenario shown above, when a train is arriving, it looks like this:

The red train can't move at all because it can't reserve every tile along the path it wants to take. However, once the blue train has arrived at its signal, the red train can immediately depart through the track segment that the blue train is on because the tiles the red train needs to cross are no longer reserved.