diff -r 59ed103fff61 -r 257de56ddd2f src/tunnelbridge_cmd.cpp
--- a/src/tunnelbridge_cmd.cpp	Sat May 26 17:06:45 2007 +0000
+++ b/src/tunnelbridge_cmd.cpp	Sat May 26 20:30:40 2007 +0000
@@ -304,6 +304,9 @@
 		cost = (bridge_len + 1) * _price.clear_bridge; // The cost of clearing the current bridge.
 		replace_bridge = true;
 		replaced_bridge_type = GetBridgeType(tile_start);
+
+		/* Do not remove road types when upgrading a bridge */
+		roadtypes |= GetRoadTypes(tile_start);
 	} else {
 		/* Build a new bridge. */