AIRoad.RemoveRoad() failing

[MinchinWeb]

I was trying to remove extra roads using AIRoad.RemoveRoad(), but it kept leaving little bits of road, almost all (all?) on steep slopes. The road would have originally been a straight line down the hill, with the road tiles removed in a random order. Using AIRoad.RemoveRoadFull() seems to fix it. Is this a feature, or a bug?

[Yexo]

It's a bug of your AI, not a big in OpenTTD. The upper part of a sloped road tile can't be removed without the lower part of the same tile. If you use AIRoad,RemoveRoad() in a random order, you'll try to remove the upper part of a tile before the lower part of that tile. That'll fail partially, so the upper part of that tile stays while the lower part of the adjacent tile will be removed (and AIRoad.RemoveRoad() returns True since part of the road is removed).Later you'll remove the lower part of the same tile, which will succeed, leaving a half-tile road at the upper half of the tile as you can see in your screenshots. Using AIRoad.RemoveRoadFull() is one solution, however using that you might remove a roadbit too much at the connecting road. Another solution that works in every case would to first call AIRoad.RemoveRoad() form the tile connection the stray road tile to the existing road and call AIRoad.RmoeveRoadFull() for the rest of the road you want to remove.

[MinchinWeb]

If I were to use RemoveRoad() going up the hill, would that solve the problem (thus removing the lower part of the road before the top part)?

[Yexo]

Yes. Be aware of roads that go uphill, downhill and uphill again.