diff --git a/src/road.cpp b/src/road.cpp
index 399971c..3f0d436 100644
--- a/src/road.cpp
+++ b/src/road.cpp
@@ -247,3 +247,54 @@ bool RoadTypeIdentifier::UnpackIfValid(uint32 data)
 	assert(ret);
 	return result;
 }
+
+/**
+ * Returns the available RoadSubTypes for the provided RoadType
+ * @param rt the RoadType to filter
+ * @param c the company to check the roadtype against
+ * @param only_existing whether to return only currently introduced vehicles or also future ones
+ * @returns the existing RoadSubTypes
+ */
+RoadSubTypes ExistingRoadSubTypesForRoadType(RoadType rt, CompanyID c, bool only_existing = false)
+{
+	RoadSubTypes known_roadsubtypes = ROADSUBTYPES_NONE;
+	RoadSubTypes available_roadsubtypes = ROADSUBTYPES_NONE;
+
+	/* Road is always visible and available. */
+	if (rt == ROADTYPE_ROAD) known_roadsubtypes |= ROADSUBTYPES_NORMAL; // TODO
+
+	/* 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;
+
+		known_roadsubtypes |= GetRoadTypeInfo(rtid)->introduces_roadtypes;
+	}
+
+	if (!only_existing) {
+		/* Get the date introduced roadtypes as well. */
+		known_roadsubtypes = AddDateIntroducedRoadTypes(rt, known_roadsubtypes, MAX_DAY);
+	}
+
+	const Company *company = Company::GetIfValid(c);
+
+	/* If it's not used ever, don't show it to the user. */
+	RoadTypeIdentifier rtid;
+	FOR_ALL_SORTED_ROADTYPES(rtid, rt) {
+		if (!HasBit(known_roadsubtypes, rtid.subtype)) continue;
+
+		if (company != NULL) {
+			if (only_existing && !HasBit(company->avail_roadtypes[rtid.basetype], rtid.subtype)) {
+				continue;
+			}
+		}
+
+		SetBit(available_roadsubtypes, rtid.subtype);
+	}
+	
+	return available_roadsubtypes;
+}