Index: trunk/data/validator/geometry.mapcss
===================================================================
--- trunk/data/validator/geometry.mapcss	(revision 7468)
+++ trunk/data/validator/geometry.mapcss	(revision 7645)
@@ -72,2 +72,7 @@
   throwWarning: tr("{0} inside {1}", concat("power=", tag("power")), concat("power=", tag("power")));
 }
+
+way[route=bus] {
+  /* see #10252 */
+  throwWarning: tr("{0} on a way. Should be used in a relation", "{0.tag}"); 
+}