disallow_junctions.patch

diff --git a/src/road.h b/src/road.h
index 0defe74..3bde774 100644
--- a/src/road.h
+++ b/src/road.h
@@ -25,9 +25,11 @@
 /** Roadtype flags. Starts with RO instead of R because R is used for rails */
 enum RoadTypeFlags {
 	ROTF_CATENARY = 0,                   ///< Bit number for adding catenary
+	ROTF_DISALLOW_JUNCTIONS = 1,         ///< Bit number for disallowing junctions (only build straight line or curve)
 
 	ROTFB_NONE = 0,                      ///< All flags cleared.
 	ROTFB_CATENARY = 1 << ROTF_CATENARY, ///< Value for drawing a catenary.
+	ROTFB_DISALLOW_JUNCTIONS = 1 << ROTF_DISALLOW_JUNCTIONS, ///< Value for disallowing junctions.
 };
 DECLARE_ENUM_AS_BIT_SET(RoadTypeFlags)
 
diff --git a/src/road_cmd.cpp b/src/road_cmd.cpp
index 6687aa4..bf232e0 100644
--- a/src/road_cmd.cpp
+++ b/src/road_cmd.cpp
@@ -626,6 +626,7 @@ CommandCost CmdBuildRoad(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 
 	RoadBits existing = ROAD_NONE;
 	RoadBits other_bits = ROAD_NONE;
+	RoadTypeIdentifiers existing_rtids;
 
 	/* Road pieces are max 4 bitset values (NE, NW, SE, SW) and town can only be non-zero
 	 * if a non-company is building the road */
@@ -666,8 +667,15 @@ CommandCost CmdBuildRoad(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 
 					other_bits = GetOtherRoadBits(tile, rtid.basetype);
 					if (!HasTileRoadType(tile, rtid.basetype)) break;
-
+					
+					existing_rtids = RoadTypeIdentifiers::FromTile(tile);
 					existing = GetRoadBits(tile, rtid.basetype);
+					bool disallow_junctions = HasBit(GetRoadTypeInfo(rtid)->flags, ROTF_DISALLOW_JUNCTIONS)
+						|| HasBit(GetRoadTypeInfo(existing_rtids.GetType(rtid.basetype))->flags, ROTF_DISALLOW_JUNCTIONS);
+					if (rtid.IsRoad() && IsRoadJunction(existing | pieces) && disallow_junctions) {
+						/* Some roads disallow junctions */
+						return_cmd_error(STR_ERROR_ONEWAY_ROADS_CAN_T_HAVE_JUNCTION); // TODO
+					}
 					bool crossing = !IsStraightRoad(existing | pieces);
 					if (rtid.IsRoad() && (GetDisallowedRoadDirections(tile) != DRD_NONE || toggle_drd != DRD_NONE) && crossing) {
 						/* Junctions cannot be one-way */
diff --git a/src/road_func.h b/src/road_func.h
index d4828cb..a611fb0 100644
--- a/src/road_func.h
+++ b/src/road_func.h
@@ -123,6 +123,12 @@ static inline bool IsStraightRoad(RoadBits r)
 	return (r == ROAD_X || r == ROAD_Y);
 }
 
+static inline bool IsRoadJunction(RoadBits r)
+{
+	assert(IsValidRoadBits(r));
+	return (CountBits(r) > 2);
+}
+
 /**
  * Create the road-part which belongs to the given DiagDirection
  *