Index: /trunk/data/validator/highway.mapcss
===================================================================
--- /trunk/data/validator/highway.mapcss	(revision 15284)
+++ /trunk/data/validator/highway.mapcss	(revision 15285)
@@ -53,5 +53,9 @@
 }
 
-way.major_road[!ref][!destination:ref][noref!=yes][junction!=roundabout] {
+/* #17970 */
+relation[type=route][route=road][ref] > way.major_road {
+  set road_route_has_ref;
+}
+way.major_road!.road_route_has_ref[!ref][!destination:ref][noref!=yes][junction!=roundabout] {
   throwOther: tr("highway without a reference");
   group: tr("missing tag");