diff --git a/src/road.cpp b/src/road.cpp
index 399971c..7205bc1 100644
--- a/src/road.cpp
+++ b/src/road.cpp
@@ -247,3 +247,33 @@ bool RoadTypeIdentifier::UnpackIfValid(uint32 data)
 	assert(ret);
 	return result;
 }
+
+/**
+ * Returns the available RoadSubTypes for the provided RoadType
+ * @param rt the RoadType to filter
+ * @param only_existing whether to return only currently introduced vehicles or also future ones
+ * @returns the existing RoadSubTypes
+ */
+RoadSubTypes ExistingRoadSubTypesForRoadType(RoadType rt, bool only_existing = false)
+{
+	RoadSubTypes used_roadsubtypes = ROADSUBTYPES_NONE;
+
+	/* Find used roadtypes */
+	Engine *e;
+	FOR_ALL_ENGINES_OF_TYPE(e, VEH_ROAD) {
+		/* Check if the subtype can be used in the current climate */
+		if (!HasBit(e->info.climates,  _settings_game.game_creation.landscape)) continue;
+
+		RoadTypeIdentifier rtid = e->GetRoadType();
+		if (rtid.basetype != rt) continue;
+
+		used_roadsubtypes |= GetRoadTypeInfo(rtid)->introduces_roadtypes;
+	}
+
+	if (!only_existing) {
+		/* Get the date introduced roadtypes as well. */
+		used_roadsubtypes = AddDateIntroducedRoadTypes(rt, used_roadsubtypes, MAX_DAY);
+	}
+
+	return used_roadsubtypes;
+}