Index: /trunk/src/org/openstreetmap/josm/data/validation/tests/Highways.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/validation/tests/Highways.java	(revision 18272)
+++ /trunk/src/org/openstreetmap/josm/data/validation/tests/Highways.java	(revision 18273)
@@ -213,4 +213,7 @@
         carsWays = 0;
 
+        if (n.hasTag("highway","crossing") && !n.hasKey("crossing"))
+            return; // see #20905 handled by mapcss test
+
         for (Way w : n.getParentWays()) {
             String highway = w.get(HIGHWAY);