--- a/src/openttd.cpp	Tue Feb 13 20:57:02 2007 +0000
+++ b/src/openttd.cpp	Tue Feb 13 22:27:27 2007 +0000
@@ -1458,7 +1458,7 @@
 			if (v->type == VEH_Train) {
 				v->u.rail.track = TRACK_BIT_WORMHOLE;
 			} else {
-				v->u.road.state = 0xFF;
+				v->u.road.state = RVSB_WORMHOLE;
 			}
 		}
 	}

--- a/src/roadveh_cmd.cpp	Tue Feb 13 20:57:02 2007 +0000
+++ b/src/roadveh_cmd.cpp	Tue Feb 13 22:27:27 2007 +0000
@@ -74,6 +74,23 @@
 	TRACKDIR_BIT_RIGHT_S | TRACKDIR_BIT_LOWER_E | TRACKDIR_BIT_Y_SE
 };
 
+/** Converts the exit direction of a depot to trackdir the vehicle is going to drive to */
+static const Trackdir _roadveh_depot_exit_trackdir[DIAGDIR_END] = {
+	TRACKDIR_X_NE, TRACKDIR_Y_SE, TRACKDIR_X_SW, TRACKDIR_Y_NW
+};
+
+/** Checks whether the trackdir means that we are reversing */
+static bool IsReversingRoadTrackdir(Trackdir dir)
+{
+	return (dir & 0x07) >= 6;
+}
+
+/** Checks whether the given trackdir is a straight road */
+static bool IsStraightRoadTrackdir(Trackdir dir)
+{
+	return (dir & 0x06) == 0;
+}
+
 int GetRoadVehImage(const Vehicle* v, Direction direction)
 {
 	int img = v->spritenum;
@@ -161,7 +178,7 @@
 		v->z_pos = GetSlopeZ(x,y);
 		v->z_height = 6;
 
-		v->u.road.state = 254;
+		v->u.road.state = RVSB_IN_DEPOT;
 		v->vehstatus = VS_HIDDEN|VS_STOPPED|VS_DEFPAL;
 
 		v->spritenum = rvi->image_index;
@@ -452,7 +469,7 @@
 			v->u.road.crashed_ctr != 0 ||
 			v->breakdown_ctr != 0 ||
 			v->u.road.overtaking != 0 ||
-			v->u.road.state == 255 ||
+			v->u.road.state == RVSB_WORMHOLE ||
 			IsRoadVehInDepot(v) ||
 			v->cur_speed < 5) {
 		return CMD_ERROR;
@@ -502,7 +519,7 @@
 	rs->SetEntranceBusy(false);
 
 	/* Free the parking bay */
-	rs->FreeBay(HASBIT(v->u.road.state, 1) ? 1 : 0);
+	rs->FreeBay(HASBIT(v->u.road.state, RVS_USING_SECOND_BAY) ? 1 : 0);
 }
 
 static void RoadVehDelete(Vehicle *v)
@@ -607,7 +624,7 @@
 {
 	TileIndex tile;
 
-	if (v->u.road.state == 255) return;
+	if (v->u.road.state == RVSB_WORMHOLE) return;
 
 	tile = v->tile;
 
@@ -875,7 +892,7 @@
 
 	// Clamp
 	spd = min(spd, v->max_speed);
-	if (v->u.road.state == 255) spd = min(spd, SetSpeedLimitOnBridge(v));
+	if (v->u.road.state == RVSB_WORMHOLE) spd = min(spd, SetSpeedLimitOnBridge(v));
 
 	//updates statusbar only if speed have changed to save CPU time
 	if (spd != v->cur_speed) {
@@ -966,7 +983,8 @@
 
 	if (v->direction != u->direction || !(v->direction & 1)) return;
 
-	if (v->u.road.state >= 32 || (v->u.road.state & 7) > 1) return;
+	/* Check if vehicle is in a road stop, depot, tunnel or bridge or not on a straight road */
+	if (v->u.road.state >= RVS_IN_ROAD_STOP || !IsStraightRoadTrackdir((Trackdir)(v->u.road.state & RVSB_TRACKDIR_MASK))) return;
 
 	tt = GetTileTrackStatus(v->tile, TRANSPORT_ROAD) & 0x3F;
 	if ((tt & 3) == 0) return;
@@ -1242,11 +1260,6 @@
 	15, 15, 11, 11
 };
 
-/** Converts the exit direction of a depot to trackdir the vehicle is going to drive to */
-static const Trackdir _roadveh_depot_exit_trackdir[DIAGDIR_END] = {
-	TRACKDIR_X_NE, TRACKDIR_Y_SE, TRACKDIR_X_SW, TRACKDIR_Y_NW
-};
-
 static void RoadVehController(Vehicle *v)
 {
 	Direction new_dir;
@@ -1327,11 +1340,8 @@
 		if (++v->u.road.overtaking_ctr >= 35)
 			/* If overtaking just aborts at a random moment, we can have a out-of-bound problem,
 			 *  if the vehicle started a corner. To protect that, only allow an abort of
-			 *  overtake if we are on straight road, which are the 8 states below */
-			if (v->u.road.state == 0  || v->u.road.state == 1  ||
-					v->u.road.state == 8  || v->u.road.state == 9  ||
-					v->u.road.state == 16 || v->u.road.state == 17 ||
-					v->u.road.state == 24 || v->u.road.state == 25) {
+			 *  overtake if we are on straight roads */
+			if (v->u.road.state < RVSB_IN_ROAD_STOP && IsStraightRoadTrackdir((Trackdir)v->u.road.state)) {
 				v->u.road.overtaking = 0;
 			}
 	}
@@ -1339,7 +1349,7 @@
 	/* Save old vehicle position to use at end of move to set viewport area dirty */
 	BeginVehicleMove(v);
 
-	if (v->u.road.state == 255) {
+	if (v->u.road.state == RVSB_WORMHOLE) {
 		/* Vehicle is on a bridge or in a tunnel */
 		GetNewVehiclePosResult gp;
 
@@ -1367,7 +1377,7 @@
 	}
 
 	/* Get move position data for next frame */
-	rd = _road_drive_data[(v->u.road.state + (_opt.road_side << 4)) ^ v->u.road.overtaking][v->u.road.frame + 1];
+	rd = _road_drive_data[(v->u.road.state + (_opt.road_side << RVS_DRIVE_SIDE)) ^ v->u.road.overtaking][v->u.road.frame + 1];
 
 	if (rd.x & 0x80) {
 		/* Vehicle is moving to the next tile */
@@ -1384,7 +1394,7 @@
 		}
 
 again:
-		if ((dir & 7) >= 6) {
+		if (IsReversingRoadTrackdir(dir)) {
 			/* Turning around */
 			tile = v->tile;
 		}
@@ -1406,12 +1416,12 @@
 				return;
 			}
 			/* Try an about turn to re-enter the previous tile */
-			dir = _road_reverse_table[rd.x&3];
+			dir = _road_reverse_table[rd.x & 3];
 			goto again;
 		}
 
-		if (IS_BYTE_INSIDE(v->u.road.state, 0x20, 0x30) && IsTileType(v->tile, MP_STATION)) {
-			if ((dir & 7) >= 6) {
+		if (IS_BYTE_INSIDE(v->u.road.state, RVSB_IN_ROAD_STOP, RVSB_IN_ROAD_STOP_END) && IsTileType(v->tile, MP_STATION)) {
+			if (IsReversingRoadTrackdir(dir)) {
 				/* New direction is trying to turn vehicle around.
 				 * We can't turn at the exit of a road stop so wait.*/
 				v->cur_speed = 0;
@@ -1422,7 +1432,7 @@
 				RoadStop *rs = GetRoadStopByTile(v->tile, GetRoadStopType(v->tile));
 
 				/* Vehicle is leaving a road stop tile, mark bay as free and clear the usage bit */
-				rs->FreeBay(HASBIT(v->u.road.state, 1) ? 1 : 0);
+				rs->FreeBay(HASBIT(v->u.road.state, RVS_USING_SECOND_BAY) ? 1 : 0);
 				rs->SetEntranceBusy(false);
 			}
 		}
@@ -1475,7 +1485,7 @@
 		}
 
 		/* Set vehicle to second frame on the tile */
-		v->u.road.state = tmp & ~16;
+		CLRBIT(v->u.road.state, RVS_DRIVE_SIDE);
 		v->u.road.frame = 1;
 
 		if (newdir != v->direction) {
@@ -1495,7 +1505,7 @@
 
 	new_dir = RoadVehGetSlidingDirection(v, x, y);
 
-	if (!IS_BYTE_INSIDE(v->u.road.state, 0x20, 0x30)) {
+	if (!IS_BYTE_INSIDE(v->u.road.state, RVSB_IN_ROAD_STOP, RVSB_IN_ROAD_STOP_END)) {
 		/* Vehicle is not in a road stop.
 		 * Check for another vehicle to overtake */
 		Vehicle* u = RoadVehFindCloseTo(v, x, y, new_dir);
@@ -1524,8 +1534,8 @@
 		}
 	}
 
-	if (v->u.road.state >= 0x20 &&
-			_road_veh_data_1[v->u.road.state - 0x20 + (_opt.road_side<<4)] == v->u.road.frame) {
+	if (v->u.road.state >= RVSB_IN_ROAD_STOP &&
+			_road_veh_data_1[v->u.road.state - RVSB_IN_ROAD_STOP + (_opt.road_side << RVS_DRIVE_SIDE)] == v->u.road.frame) {
 		RoadStop *rs = GetRoadStopByTile(v->tile, GetRoadStopType(v->tile));
 		Station* st = GetStationByTile(v->tile);
 

--- a/src/station_cmd.cpp	Tue Feb 13 20:57:02 2007 +0000
+++ b/src/station_cmd.cpp	Tue Feb 13 22:27:27 2007 +0000
@@ -2222,7 +2222,7 @@
 			}
 		}
 	} else if (v->type == VEH_Road) {
-		if (v->u.road.state < 16 && !HASBIT(v->u.road.state, 2) && v->u.road.frame == 0) {
+		if (v->u.road.state < RVSB_IN_ROAD_STOP && v->u.road.frame == 0) {
 			if (IsRoadStop(tile)) {
 				/* Attempt to allocate a parking bay in a road stop */
 				RoadStop *rs = GetRoadStopByTile(tile, GetRoadStopType(tile));
@@ -2230,11 +2230,11 @@
 				/* Check if station is busy or if there are no free bays. */
 				if (rs->IsEntranceBusy() || !rs->HasFreeBay()) return VETSB_CANNOT_ENTER;
 
-				v->u.road.state += 32;
+				SETBIT(v->u.road.state, RVS_IN_ROAD_STOP);
 
 				/* Allocate a bay and update the road state */
 				uint bay_nr = rs->AllocateBay();
-				SB(v->u.road.state, 1, 1, bay_nr);
+				SB(v->u.road.state, RVS_USING_SECOND_BAY, 1, bay_nr);
 
 				/* Mark the station entrace as busy */
 				rs->SetEntranceBusy(true);

--- a/src/tunnelbridge_cmd.cpp	Tue Feb 13 20:57:02 2007 +0000
+++ b/src/tunnelbridge_cmd.cpp	Tue Feb 13 22:27:27 2007 +0000
@@ -1250,7 +1250,10 @@
 static const byte _tunnel_fractcoord_3[4]    = {0x82, 0x88, 0x86, 0x48};
 static const byte _exit_tunnel_track[4]      = {1, 2, 1, 2};
 
-static const byte _road_exit_tunnel_state[4] = {8, 9, 0, 1};
+/** Get the trackdir of the exit of a tunnel */
+static const Trackdir _road_exit_tunnel_state[DIAGDIR_END] = {
+	TRACKDIR_X_SW, TRACKDIR_Y_NW, TRACKDIR_X_NE, TRACKDIR_Y_SE
+};
 static const byte _road_exit_tunnel_frame[4] = {2, 7, 9, 4};
 
 static const byte _tunnel_fractcoord_4[4]    = {0x52, 0x85, 0x98, 0x29};
@@ -1304,11 +1307,11 @@
 			vdir = DirToDiagDir(v->direction);
 
 			// Enter tunnel?
-			if (v->u.road.state != 0xFF && dir == vdir) {
+			if (v->u.road.state != RVSB_WORMHOLE && dir == vdir) {
 				if (fc == _tunnel_fractcoord_4[dir] ||
 						fc == _tunnel_fractcoord_5[dir]) {
 					v->tile = tile;
-					v->u.road.state = 0xFF;
+					v->u.road.state = RVSB_WORMHOLE;
 					v->vehstatus |= VS_HIDDEN;
 					return VETSB_ENTERED_WORMHOLE;
 				} else {
@@ -1354,7 +1357,7 @@
 				CLRBIT(v->u.rail.flags, VRF_GOINGUP);
 				CLRBIT(v->u.rail.flags, VRF_GOINGDOWN);
 			} else {
-				v->u.road.state = 0xFF;
+				v->u.road.state = RVSB_WORMHOLE;
 			}
 			return VETSB_ENTERED_WORMHOLE;
 		} else if (DirToDiagDir(v->direction) == ReverseDiagDir(dir)) {
@@ -1365,7 +1368,7 @@
 					return VETSB_ENTERED_WORMHOLE;
 				}
 			} else {
-				if (v->u.road.state == 0xFF) {
+				if (v->u.road.state == RVSB_WORMHOLE) {
 					v->u.road.state = _road_exit_tunnel_state[dir];
 					v->u.road.frame = 0;
 					return VETSB_ENTERED_WORMHOLE;

--- a/src/vehicle.cpp	Tue Feb 13 20:57:02 2007 +0000
+++ b/src/vehicle.cpp	Tue Feb 13 22:27:27 2007 +0000
@@ -2524,7 +2524,7 @@
 
 		case VEH_Road:
 			InvalidateWindowClasses(WC_ROADVEH_LIST);
-			v->u.road.state = 254;
+			v->u.road.state = RVSB_IN_DEPOT;
 			break;
 
 		case VEH_Ship:

--- a/src/vehicle.h	Tue Feb 13 20:57:02 2007 +0000
+++ b/src/vehicle.h	Tue Feb 13 22:27:27 2007 +0000
@@ -27,6 +27,37 @@
 	VETSB_CANNOT_ENTER     = 1 << VETS_CANNOT_ENTER,     ///< The vehicle cannot enter the tile
 };
 
+/** Road vehicle states */
+enum RoadVehicleStates {
+	/*
+	 * Lower 4 bits are used for vehicle track direction. (Trackdirs)
+	 * When in a road stop (bit 5 set) these bits give the
+	 * track direction of the entry to the road stop.
+	 * As the entry direction will always be a diagonal
+	 * direction (X_NE, Y_SE, X_SW or Y_NW) only bits 0 and 3
+	 * are needed to hold this direction. Bit 1 is then used to show
+	 * that the vehicle is using the second road stop bay.
+	 */
+
+	/* Numeric values */
+	RVSB_IN_DEPOT                = 0xFE,                      ///< The vehicle is in a depot
+	RVSB_WORMHOLE                = 0xFF,                      ///< The vehicle is in a tunnel and/or bridge
+
+	/* Bit numbers */
+	RVS_USING_SECOND_BAY         =    1,                      ///< Only used while in a road stop
+	RVS_DRIVE_SIDE               =    4,                      ///< Only used when retrieving move data and for turning vehicles
+	RVS_IN_ROAD_STOP             =    5,                      ///< The vehicle is in a road stop
+
+	/* Bit sets of the above specified bits */
+	RVSB_USING_SECOND_BAY        = 1 << RVS_USING_SECOND_BAY, ///< Only used while in a road stop
+	RVSB_DRIVE_SIDE              = 1 << RVS_DRIVE_SIDE,       ///< Only used when retrieving move data and for turning vehicles
+	RVSB_IN_ROAD_STOP            = 1 << RVS_IN_ROAD_STOP,     ///< The vehicle is in a road stop
+	RVSB_IN_ROAD_STOP_END        = RVSB_IN_ROAD_STOP + TRACKDIR_END,
+
+	RVSB_TRACKDIR_MASK           = 0x0F,                      ///< The mask used to extract track dirs
+	RVSB_ROAD_STOP_TRACKDIR_MASK = 0x09                       ///< Only bits 0 and 3 are used to encode the trackdir for road stops
+};
+
 enum {
 	VEH_Train,
 	VEH_Road,
@@ -136,7 +167,7 @@
 } VehicleAir;
 
 typedef struct VehicleRoad {
-	byte state;
+	byte state;             /// @see RoadVehicleStates
 	byte frame;
 	uint16 blocked_ctr;
 	byte overtaking;