From 8e5371eec40f6d4d15baecc3f65d04db60573ab7 Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Sun, 26 Feb 2023 14:45:40 +0000
Subject: [PATCH] Public roads: Fix handling of non-trivial foundations

---
 src/road.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/road.cpp b/src/road.cpp
index deda3cfd31..880416839c 100644
--- a/src/road.cpp
+++ b/src/road.cpp
@@ -576,6 +576,12 @@ static bool IsValidNeighbourOfPreviousTile(const TileIndex tile, const TileIndex
 		desc.z = desc.tile_z;
 		desc.slope = GetFoundationSlopeFromTileSlope(t, desc.tile_slope, &desc.z);
 
+		if (desc.slope == desc.tile_slope && desc.slope != SLOPE_FLAT && HasBit(VALID_LEVEL_CROSSING_SLOPES, desc.slope)) {
+			/* Synthesise a trivial flattening foundation */
+			desc.slope = SLOPE_FLAT;
+			desc.z++;
+		}
+
 		return desc;
 	};
 	const slope_desc sd = get_slope_info(tile);