diff --git a/src/saveload/afterload.cpp b/src/saveload/afterload.cpp
index 94529fc456..288faf2373 100644
--- a/src/saveload/afterload.cpp
+++ b/src/saveload/afterload.cpp
@@ -2046,7 +2046,7 @@ bool AfterLoadGame()
 						return false;
 					}
 
-					const Tunnel *t = new Tunnel(start_tile, end_tile, false);
+					const Tunnel *t = new Tunnel(start_tile, end_tile, TileHeight(start_tile), false);
 
 					SetTunnelIndex(start_tile, t->index);
 					SetTunnelIndex(end_tile, t->index);
@@ -2055,7 +2055,6 @@ bool AfterLoadGame()
 		}
 	}
 
-
 	/* Move the signal variant back up one bit for PBS. We don't convert the old PBS
 	 * format here, as an old layout wouldn't work properly anyway. To be safe, we
 	 * clear any possible PBS reservations as well. */
diff --git a/src/saveload/tunnel_sl.cpp b/src/saveload/tunnel_sl.cpp
index 470de84590..d50b4bcd83 100644
--- a/src/saveload/tunnel_sl.cpp
+++ b/src/saveload/tunnel_sl.cpp
@@ -20,6 +20,7 @@
 static const SaveLoad _tunnel_desc[] = {
 	 SLE_CONDVAR(Tunnel, tile_n,           SLE_UINT32,             0, SL_MAX_VERSION),
 	 SLE_CONDVAR(Tunnel, tile_s,           SLE_UINT32,             0, SL_MAX_VERSION),
+	 SLE_CONDVAR(Tunnel, height,            SLE_UINT8,             0, SL_MAX_VERSION),
 	 SLE_CONDVAR(Tunnel, is_chunnel,         SLE_BOOL,             0, SL_MAX_VERSION),
 	 SLE_END()
 };
diff --git a/src/tunnel_base.h b/src/tunnel_base.h
index 92408abde8..06196c2359 100644
--- a/src/tunnel_base.h
+++ b/src/tunnel_base.h
@@ -24,12 +24,13 @@ struct Tunnel : TunnelPool::PoolItem<&_tunnel_pool> {
 
 	TileIndex tile_n; // North tile of tunnel.
 	TileIndex tile_s; // South tile of tunnel.
-	bool is_chunnel;
+	uint8 height;     // Tunnel height
+	bool is_chunnel;  // Whether this tunnel is a chunnel
 
 	Tunnel() {}
 	~Tunnel();
 
-	Tunnel(TileIndex tile_n, TileIndex tile_s, bool is_chunnel) : tile_n(tile_n), tile_s(tile_s), is_chunnel(is_chunnel)
+	Tunnel(TileIndex tile_n, TileIndex tile_s, uint8 height, bool is_chunnel) : tile_n(tile_n), tile_s(tile_s), height(height), is_chunnel(is_chunnel)
 	{
 		this->UpdateIndexes();
 	}
diff --git a/src/tunnel_map.cpp b/src/tunnel_map.cpp
index cd049f7397..7b546848a4 100644
--- a/src/tunnel_map.cpp
+++ b/src/tunnel_map.cpp
@@ -22,6 +22,21 @@ TunnelPool _tunnel_pool("Tunnel");
 INSTANTIATE_POOL_METHODS(Tunnel)
 
 static std::unordered_map<TileIndex, TunnelID> tunnel_tile_index_map;
+static std::unordered_multimap<uint64, Tunnel*> tunnel_axis_height_index;
+
+static uint64 GetTunnelAxisHeightCacheKey(TileIndex tile, uint8 height, bool y_axis) {
+	if (y_axis) {
+		// tunnel extends along Y axis (DIAGDIR_SE from north end), has same X values
+		return TileX(tile) | (((uint64) height) << 24) | (((uint64) 1) << 32);
+	} else {
+		// tunnel extends along X axis (DIAGDIR_SW from north end), has same Y values
+		return TileY(tile) | (((uint64) height) << 24);
+	}
+}
+
+static inline uint64 GetTunnelAxisHeightCacheKey(const Tunnel* t) {
+	return GetTunnelAxisHeightCacheKey(t->tile_n, t->height, t->tile_s - t->tile_n > MapMaxX());
+}
 
 /**
  * Clean up a tunnel tile
@@ -34,6 +49,17 @@ Tunnel::~Tunnel()
 		tunnel_tile_index_map.erase(this->tile_n);
 		tunnel_tile_index_map.erase(this->tile_s);
 	}
+
+	auto range = tunnel_axis_height_index.equal_range(GetTunnelAxisHeightCacheKey(this));
+	bool have_erased = false;
+	for (auto it = range.first; it != range.second; ++it) {
+		if (it->second == this) {
+			tunnel_axis_height_index.erase(it);
+			have_erased = true;
+			break;
+		}
+	}
+	assert(have_erased);
 }
 
 /**
@@ -45,6 +71,8 @@ void Tunnel::UpdateIndexes()
 		tunnel_tile_index_map[this->tile_n] = this->index;
 		tunnel_tile_index_map[this->tile_s] = this->index;
 	}
+
+	tunnel_axis_height_index.emplace(GetTunnelAxisHeightCacheKey(this), this);
 }
 
 /**
@@ -53,6 +81,7 @@ void Tunnel::UpdateIndexes()
 void Tunnel::PreCleanPool()
 {
 	tunnel_tile_index_map.clear();
+	tunnel_axis_height_index.clear();
 }
 
 TunnelID GetTunnelIndexByLookup(TileIndex t)
@@ -74,6 +103,24 @@ TileIndex GetOtherTunnelEnd(TileIndex tile)
 	return t->tile_n == tile ? t->tile_s : t->tile_n;
 }
 
+static inline bool IsTunnelInWaySingleAxis(TileIndex tile, int z, bool chunnel_allowed, bool y_axis, TileIndexDiff tile_diff)
+{
+	const auto tunnels = tunnel_axis_height_index.equal_range(GetTunnelAxisHeightCacheKey(tile, z, y_axis));
+	for (auto it = tunnels.first; it != tunnels.second; ++it) {
+		const Tunnel *t = it->second;
+		if (t->tile_n > tile || tile > t->tile_s) continue;
+
+		if (t->is_chunnel && chunnel_allowed) {
+			/* Only if tunnel was built over water is terraforming is allowed between portals. */
+			const TileIndexDiff delta = tile_diff * 4;  // 4 tiles ramp.
+			if (tile < t->tile_n + delta || t->tile_s - delta < tile) return true;
+			continue;
+		}
+		return true;
+	}
+	return false;
+}
+
 /**
  * Is there a tunnel in the way in any direction?
  * @param tile the tile to search from.
@@ -83,26 +130,5 @@ TileIndex GetOtherTunnelEnd(TileIndex tile)
  */
 bool IsTunnelInWay(TileIndex tile, int z, bool chunnel_allowed)
 {
-	uint x = TileX(tile);
-	uint y = TileY(tile);
-
-	Tunnel *t;
-	FOR_ALL_TUNNELS(t)  {
-		if (t->tile_n > tile || tile > t->tile_s) continue;
-
-		if (t->tile_s - t->tile_n > MapMaxX()){
-			if (TileX(t->tile_n) != x || (int)TileHeight(t->tile_n) != z) continue; // dir DIAGDIR_SE
-		} else {
-			if (TileY(t->tile_n) != y || (int)TileHeight(t->tile_n) != z) continue; // dir DIAGDIR_SW
-		}
-
-		if (t->is_chunnel && chunnel_allowed) {
-			/* Only if tunnel was build over water terraforming is allowed between portals. */
-			TileIndexDiff delta = GetTunnelBridgeDirection(t->tile_n) == DIAGDIR_SE ? TileOffsByDiagDir(DIAGDIR_SE) * 4 : 4;  // 4 tiles ramp.
-			if (tile < t->tile_n + delta || t->tile_s - delta < tile) return true;
-			continue;
-		}
-		return true;
-	}
-	return false;
+	return IsTunnelInWaySingleAxis(tile, z, chunnel_allowed, false, 1) || IsTunnelInWaySingleAxis(tile, z, chunnel_allowed, true, TileOffsByDiagDir(DIAGDIR_SE));
 }
diff --git a/src/tunnelbridge_cmd.cpp b/src/tunnelbridge_cmd.cpp
index 0bd2e54bb8..30df9ce9ef 100644
--- a/src/tunnelbridge_cmd.cpp
+++ b/src/tunnelbridge_cmd.cpp
@@ -814,7 +814,7 @@ CommandCost CmdBuildTunnel(TileIndex start_tile, DoCommandFlag flags, uint32 p1,
 		if(start_tile > end_tile) Swap(tn, ts);
 
 		if (!Tunnel::CanAllocateItem()) return_cmd_error(STR_ERROR_TUNNEL_TOO_MANY);
-		const Tunnel *t = new Tunnel(tn, ts, is_chunnel);
+		const Tunnel *t = new Tunnel(tn, ts, TileHeight(tn), is_chunnel);
 
 		if (transport_type == TRANSPORT_RAIL) {
 			if (!IsTunnelTile(start_tile) && c != NULL) c->infrastructure.rail[railtype] += num_pieces;