--- a/map.c	Fri Sep 09 15:49:46 2005 +0000
+++ b/map.c	Fri Sep 09 23:14:38 2005 +0000
@@ -155,21 +155,6 @@
 	return dx > dy ? 2 * dx + dy : 2 * dy + dx;
 }
 
-uint DistanceTrack(TileIndex t0, TileIndex t1)
-{
-	const uint dx = abs(TileX(t0) - TileX(t1));
-	const uint dy = abs(TileY(t0) - TileY(t1));
-
-	const uint straightTracks = 2 * min(dx, dy); /* The number of straight (not full length) tracks */
-	/* OPTIMISATION:
-	 * Original: diagTracks = max(dx, dy) - min(dx,dy);
-	 * Proof:
-	 * (dx-dy) - straightTracks  == (min + max) - straightTracks = min + // max - 2 * min = max - min */
-	const uint diagTracks = dx + dy - straightTracks; /* The number of diagonal (full tile length) tracks. */
-
-	return diagTracks + straightTracks * STRAIGHT_TRACK_LENGTH;
-}
-
 uint DistanceFromEdge(TileIndex tile)
 {
 	const uint xl = TileX(tile);

--- a/map.h	Fri Sep 09 15:49:46 2005 +0000
+++ b/map.h	Fri Sep 09 23:14:38 2005 +0000
@@ -144,7 +144,6 @@
 uint DistanceSquare(TileIndex, TileIndex); // euclidian- or L2-Norm squared
 uint DistanceMax(TileIndex, TileIndex); // also known as L-Infinity-Norm
 uint DistanceMaxPlusManhattan(TileIndex, TileIndex); // Max + Manhattan
-uint DistanceTrack(TileIndex, TileIndex); // Returns the shortest distance one could go over tracks
 uint DistanceFromEdge(TileIndex); // shortest distance from any edge of the map
 
 

--- a/npf.c	Fri Sep 09 15:49:46 2005 +0000
+++ b/npf.c	Fri Sep 09 23:14:38 2005 +0000
@@ -25,6 +25,29 @@
 };
 
 /**
+ * Calculates the minimum distance traveled to get from t0 to t1 when only
+ * using tracks (ie, only making 45 degree turns). Returns the distance in the
+ * NPF scale, ie the number of full tiles multiplied by NPF_TILE_LENGTH to
+ * prevent rounding.
+ */
+uint NPFDistanceTrack(TileIndex t0, TileIndex t1)
+{
+	const uint dx = abs(TileX(t0) - TileX(t1));
+	const uint dy = abs(TileY(t0) - TileY(t1));
+
+	const uint straightTracks = 2 * min(dx, dy); /* The number of straight (not full length) tracks */
+	/* OPTIMISATION:
+	 * Original: diagTracks = max(dx, dy) - min(dx,dy);
+	 * Proof:
+	 * (dx+dy) - straightTracks  == (min + max) - straightTracks = min + max - 2 * min = max - min */
+	const uint diagTracks = dx + dy - straightTracks; /* The number of diagonal (full tile length) tracks. */
+
+	/* Don't factor out NPF_TILE_LENGTH below, this will round values and lose
+	 * precision */
+	return diagTracks * NPF_TILE_LENGTH + straightTracks * NPF_TILE_LENGTH * STRAIGHT_TRACK_LENGTH;
+}
+
+/**
  * Check if a rail track is the end of the line. Will also consider 1-way signals to be the end of a line.
  * @param tile The tile on which the current track is.
  * @param trackdir The (track)direction in which you want to look.
@@ -36,11 +59,11 @@
 	TileIndex dst_tile;
 	uint32 ts;
 
-	// tunnel entrance?
+	/* Can always go into a tunnel */
 	if (IsTileType(tile, MP_TUNNELBRIDGE) && (_m[tile].m5 & 0xF0)==0 && (_m[tile].m5 & 3) == exitdir)
 		return false;
 
-	// depot
+	/* Cannot go through the back of a depot */
 	if (IsTileDepotType(tile, TRANSPORT_RAIL) && (exitdir != GetDepotDirection(tile, TRANSPORT_RAIL)))
 		return true;
 
@@ -60,9 +83,14 @@
 		if (GetTileOwner(tile) != GetTileOwner(dst_tile))
 			return true;
 
+		/* Prevent us from entering a depot from behind */
 		if (IsTileDepotType(dst_tile, TRANSPORT_RAIL) && (exitdir != ReverseDiagdir(GetDepotDirection(dst_tile, TRANSPORT_RAIL))))
 			return true;
 
+		/* Prevent us from falling off a slope into a tunnel exit */
+		if (IsTileType(dst_tile, MP_TUNNELBRIDGE) && (_m[dst_tile].m5 & 0xF0)==0 && (DiagDirection)(_m[dst_tile].m5 & 3) == ReverseDiagdir(exitdir))
+				return true;
+
 		/* Check for oneway signal against us */
 		if (IsTileType(dst_tile, MP_RAILWAY) && GetRailTileType(dst_tile) == RAIL_TYPE_SIGNALS) {
 			if (HasSignalOnTrackdir(dst_tile, ReverseTrackdir(FindFirstBit2x64(ts))) && !HasSignalOnTrackdir(dst_tile, FindFirstBit2x64(ts)))
@@ -235,7 +263,7 @@
 		dist = DistanceManhattan(from, to) * NPF_TILE_LENGTH;
 	else
 		/* Ships and trains can also go diagonal, so the minimum distance is shorter */
-		dist = DistanceTrack(from, to) * NPF_TILE_LENGTH;
+		dist = NPFDistanceTrack(from, to);
 
 	DEBUG(npf, 4)("Calculating H for: (%d, %d). Result: %d", TileX(current->tile), TileY(current->tile), dist);