One-way road zoning mode

src/lang/english.txt

@@ -6264,6 +6264,7 @@ STR_ZONING_IND_UNSER                                            :Unserved indust
 STR_ZONING_TRACERESTRICT                                        :Restricted signals
 STR_ZONING_2x2_GRID                                             :2x2 town road grid
 STR_ZONING_3x3_GRID                                             :3x3 town road grid
+STR_ZONING_ONE_WAY_ROAD                                         :One way roads
 
 STR_TMPL_RPL_TITLE                                              :{WHITE}Template Replacement
 STR_TMPL_TEMPLATE_REPLACEMENT                                   :Template Replacement

src/roadveh_cmd.cpp

@@ -449,6 +449,16 @@ static bool IsOneWayRoadTile(TileIndex tile)
 	return false;
 }
 
+uint8 GetOneWayRoadTileType(TileIndex tile)
+{
+	if (IsNormalRoadTile(tile)) {
+		if (GetDisallowedRoadDirections(tile) != DRD_NONE) return 1;
+		if (IsOneWaySideJunctionRoad(tile)) return 2;
+	}
+	if (IsDriveThroughStopTile(tile) && GetDriveThroughStopDisallowedRoadDirections(tile) != DRD_NONE) return 3;
+	return 0;
+}
+
 /**
  * Turn a roadvehicle around.
  * @param tile unused

src/zoning.h

@@ -27,6 +27,7 @@ enum ZoningEvaluationMode {
 	ZEM_TRACERESTRICT, ///< Check for restricted signals
 	ZEM_2x2_GRID,      ///< Show 2x2 town road grid
 	ZEM_3x3_GRID,      ///< Show 3x3 town road grid
+	ZEM_ONE_WAY_ROAD,  ///< Show one way roads
 
 	ZEM_END,           ///< End marker
 };

src/zoning_cmd.cpp

@@ -273,6 +273,30 @@ inline SpriteID TileZoneCheckRoadGridEvaluation(TileIndex tile, uint grid_size)
 	}
 }
 
+/**
+ * Detect whether a tile is a one way road
+ *
+ * @param TileIndex tile
+ * @param Owner owner
+ * @return red if a restricted signal, nothing otherwise
+ */
+inline SpriteID TileZoneCheckOneWayRoadEvaluation(TileIndex tile)
+{
+	extern uint8 GetOneWayRoadTileType(TileIndex tile);
+
+	uint8 type = GetOneWayRoadTileType(tile);
+	switch (type) {
+		default:
+			return ZONING_INVALID_SPRITE_ID;
+		case 1:
+			return SPR_ZONING_INNER_HIGHLIGHT_LIGHT_BLUE;
+		case 2:
+			return SPR_ZONING_INNER_HIGHLIGHT_ORANGE;
+		case 3:
+			return SPR_ZONING_INNER_HIGHLIGHT_GREEN;
+	}
+}
+
 /**
  * General evaluation function; calls all the other functions depending on
  * evaluation mode.
@@ -297,6 +321,7 @@ SpriteID TileZoningSpriteEvaluation(TileIndex tile, Owner owner, ZoningEvaluatio
 		case ZEM_TRACERESTRICT: return TileZoneCheckTraceRestrictEvaluation(tile, owner);
 		case ZEM_2x2_GRID:      return TileZoneCheckRoadGridEvaluation(tile, 3);
 		case ZEM_3x3_GRID:      return TileZoneCheckRoadGridEvaluation(tile, 4);
+		case ZEM_ONE_WAY_ROAD:  return TileZoneCheckOneWayRoadEvaluation(tile);
 		default:                return ZONING_INVALID_SPRITE_ID;
 	}
 }

src/zoning_gui.cpp

@@ -42,6 +42,7 @@ static const StringID _zone_type_strings[] = {
 	STR_ZONING_TRACERESTRICT,
 	STR_ZONING_2x2_GRID,
 	STR_ZONING_3x3_GRID,
+	STR_ZONING_ONE_WAY_ROAD,
 	INVALID_STRING_ID
 };
 
@@ -56,6 +57,7 @@ static const ZoningEvaluationMode _zone_type_modes[] = {
 	ZEM_TRACERESTRICT,
 	ZEM_2x2_GRID,
 	ZEM_3x3_GRID,
+	ZEM_ONE_WAY_ROAD,
 };
 
 static ZoningEvaluationMode DropDownIndexToZoningEvaluationMode(int index)