Index: src/road_cmd.cpp
===================================================================
--- src/road_cmd.cpp	(Revision 20894)
+++ src/road_cmd.cpp	(Arbeitskopie)
@@ -1115,7 +1115,7 @@
 {
 	int x = ti->x | dx;
 	int y = ti->y | dy;
-	byte z = ti->z;
+	int32 z = ti->z;
 	if (ti->tileh != SLOPE_FLAT) z = GetSlopeZ(x, y);
 	AddSortableSpriteToDraw(img, PAL_NONE, x, y, 2, 2, h, z);
 }
Index: src/roadveh_cmd.cpp
===================================================================
--- src/roadveh_cmd.cpp	(Revision 20894)
+++ src/roadveh_cmd.cpp	(Arbeitskopie)
@@ -793,7 +793,7 @@
 	}
 }
 
-static void RoadZPosAffectSpeed(RoadVehicle *v, byte old_z)
+static void RoadZPosAffectSpeed(RoadVehicle *v, int32 old_z)
 {
 	if (old_z == v->z_pos || _settings_game.vehicle.roadveh_acceleration_model != AM_ORIGINAL) return;