# UNDF: UNDF-2026-000001008
--- a/src/simutrans/simhalt.cc
+++ b/src/simutrans/simhalt.cc
@@ -3295,14 +3295,19 @@
 	// iterate over all lines (public halt: all lines, other: only player's lines)
 	for(  uint8 i=pl_min;  i<pl_max;  i++  ) {
 		if(  player_t *player = welt->get_player(i)  ) {
 			player->simlinemgmt.get_lines(simline_t::line, &check_line);
 			for(linehandle_t const j : check_line  ) {
 				// only add unknown lines
-				if(  !registered_lines.is_contained(j)  &&  j->count_convoys() > 0  ) {
+				// Use a hash set for O(1) membership test instead of
+				// vector_tpl::is_contained O(R) linear scan per line.
+				// Previously O(L * R) where L = lines, R = registered lines.
+				if(  !registered_lines_set.get(j.get_id())  &&  j->count_convoys() > 0  ) {
 					for(schedule_entry_t const& k : j->get_schedule()->entries  ) {
 						if(  get_halt(k.pos, player) == self  ) {
 							registered_lines.append(j);
+							registered_lines_set.put(j.get_id(), true);
 							break;
 						}
 					}
 				}
 			}
 		}
 	}
-	// iterate over all convoys
-	for(convoihandle_t const cnv : welt->convoys()) {
-		// only check lineless convoys which have matching ownership and which are not yet registered
-		if(  !cnv->get_line().is_bound()  &&  (public_halt  ||  cnv->get_owner()==get_owner())  &&  !registered_convoys.is_contained(cnv)  ) {
+	// iterate over all convoys
+	// Build a temporary hash set of registered convoy IDs for O(1) lookup.
+	// Previously registered_convoys.is_contained(cnv) was O(R) linear scan
+	// called for every convoy in the world = O(C * R) total.
+	inthashtable_tpl<uint16, bool> registered_cnv_set;
+	for(convoihandle_t const cnv : registered_convoys) {
+		registered_cnv_set.put(cnv.get_id(), true);
+	}
+	for(convoihandle_t const cnv : welt->convoys()) {
+		// only check lineless convoys which have matching ownership and which are not yet registered
+		if(  !cnv->get_line().is_bound()  &&  (public_halt  ||  cnv->get_owner()==get_owner())  &&  !registered_cnv_set.get(cnv.get_id())  ) {
 			if(  const schedule_t *const schedule = cnv->get_schedule()  ) {
 				for(schedule_entry_t const& k : schedule->entries) {
 					if (get_halt(k.pos, cnv->get_owner()) == self) {
 						registered_convoys.append(cnv);
+						registered_cnv_set.put(cnv.get_id(), true);
 						break;
 					}
 				}