Index: src/map.h
===================================================================
--- src/map.h	(revision 8078)
+++ src/map.h	(working copy)
@@ -24,6 +24,7 @@
 	byte m4;
 	byte m5;
 	byte m6;
+	byte m7;
 } Tile;
 
 extern Tile* _m;
Index: src/train_cmd.cpp
===================================================================
--- src/train_cmd.cpp	(revision 8078)
+++ src/train_cmd.cpp	(working copy)
@@ -2934,6 +2934,8 @@
 
 	u = v;
 	BEGIN_ENUM_WAGONS(v)
+		/* When a vehicle crashes the presence on the track must be removed */
+		RemoveTrackMask(v->tile, v->u.rail.track);
 		v->vehstatus |= VS_CRASHED;
 	END_ENUM_WAGONS(v)
 
@@ -3018,6 +3020,19 @@
 	return NULL;
 }
 
+/**
+ * Set presence on track if the front engine enters or the last wagon leaves a tile.
+ */
+static void UpdateTrainTileCache(Vehicle *u, GetNewVehiclePosResult gp, TrackBits next_track)
+{
+	/* Only the last wagon may clear a tile */
+	if (u->next == NULL)
+		RemoveTrackMask(gp.old_tile, (TrackBits)u->u.rail.track);
+	/* Only the first may trigger it */
+	if (GetPrevVehicleInChain(u) == NULL)
+		SetTrackMask(gp.new_tile, next_track);
+}
+
 static void TrainController(Vehicle *v, bool update_image)
 {
 	Vehicle *prev;
@@ -3126,6 +3141,9 @@
 					chosen_dir = (Direction)b[2];
 				}
 
+				/* Keep the collision check updated with information */
+				UpdateTrainTileCache(v, gp, chosen_track);
+
 				/* Call the landscape function and tell it that the vehicle entered the tile */
 				r = VehicleEnterTile(v, gp.new_tile, gp.x, gp.y);
 				if (r & 0x8) {
@@ -3536,7 +3554,9 @@
 
 		do {
 			TrainController(v, true);
-			CheckTrainCollision(v);
+			if (GetTrackOverload(v->tile)) {
+				CheckTrainCollision(v);
+			}
 			if (v->cur_speed <= 0x100)
 				break;
 		} while (--j != 0);
Index: src/rail_map.h
===================================================================
--- src/rail_map.h	(revision 8078)
+++ src/rail_map.h	(working copy)
@@ -6,8 +6,8 @@
 #include "direction.h"
 #include "rail.h"
 #include "tile.h"
+#include "debug.h"
 
-
 typedef enum RailTileType {
 	RAIL_TILE_NORMAL         = 0x0,
 	RAIL_TILE_SIGNALS        = 0x40,
@@ -338,5 +338,56 @@
 	_m[t].m4 = 0;
 	_m[t].m5 = RAIL_TILE_DEPOT_WAYPOINT | RAIL_SUBTYPE_WAYPOINT | a;
 }
+/**
+ * Make trains aware to watch out for collisions
+ */
+static inline void SetTrackOverload(TileIndex t)
+{
+	DEBUG(misc, 2, "Turning on collision warning for tile %d", t);
+	/* Turn on first bit on */
+	SB(_m[t].m6, 2, 1, 1);
+}
 
+/**
+ * Make trains aware not to watch out for collisions anymore
+ */
+static inline void EndTrackOverload(TileIndex t)
+{
+	DEBUG(misc, 2, "Turning off collision warning for tile %d", t);
+	/* Turn off first bit on */
+	SB(_m[t].m6, 2, 1, 0);
+}
+
+/**
+ * Find out if collision check is needed
+ */
+static inline bool GetTrackOverload(TileIndex t)
+{
+	/* Check if track is overloaded/possible collision chance */
+	return GB(_m[t].m6, 2, 1);
+}
+
+/**
+ * Set the presence of trains in the map, if needed trigger an collision warning
+ */
+static inline void SetTrackMask(TileIndex t, TrackBits b)
+{
+	if ((_m[t].m7 & b) > 0) {
+		SetTrackOverload(t);
+	}
+	_m[t].m7 |= b;
+}
+
+/**
+ * Remove the presence of a train from the map, remove collision warning when active
+ */
+static inline void RemoveTrackMask(TileIndex t, TrackBits b)
+{
+	if (GetTrackOverload(t)) {
+		EndTrackOverload(t);
+	}
+	/* If a track on the same tile shares one or more trackbits and is not connected to the track being exited, this might be problematic, but i see no problems with this */
+	_m[t].m7 -= _m[t].m7 & b;
+}
+
 #endif /* RAIL_MAP_H */