Index: resources/styles/default/inc/access
===================================================================
--- resources/styles/default/inc/access	(revision 3646)
+++ resources/styles/default/inc/access	(working copy)
@@ -72,3 +72,7 @@
 # Check for carpool lane (they are not really supported yet so these lines are commented)
 # hov=* { add carpool='${hov}' }
 # (carpool=yes | carpool=designated | carpool=permissive | carpool=official)     { set mkgmap:carpool=yes }
+
+# Don't route through highway=construction, they are considered unusable 
+highway=construction {setaccess no}
+
Index: resources/styles/default/lines
===================================================================
--- resources/styles/default/lines	(revision 3646)
+++ resources/styles/default/lines	(working copy)
@@ -109,7 +109,7 @@
 
 # Ways that may or may not be useable
 
-# Treat ways under construction almost as highway=path
+# Treat ways under construction almost as highway=path, see also extra rule in inc/access
 highway=construction { add mkgmap:dead-end-check = false; }
 [0x16 road_class=0 road_speed=0 resolution 23]