Index: resources/data/validator/highway.mapcss
===================================================================
--- resources/data/validator/highway.mapcss	(revision 17884)
+++ resources/data/validator/highway.mapcss	(working copy)
@@ -1,3 +1,12 @@
+way[highway =~ /^(motorway|motorway_link|trunk|trunk_link|primary|primary_link|secondary|secondary_link|tertiary|tertiary_link|residential|unclassified)$/][area=yes] {
+  throwError: tr("{0} together with {1} is invalid", "{0.tag}", "{1.tag}");
+  group: tr("suspicious tag combination");
+  suggestAlternative: "area:highway=*";
+  assertMatch:   "area highway=trunk area=yes";
+  assertNoMatch: "area highway=service area=yes";
+  assertNoMatch: "way highway=trunk";
+}
+
 way[highway=~/^(motorway|trunk|primary|secondary|tertiary)$/] {
   set major_road;
 }