code: public static void setPreferredRoadType(RoadType type) {
  		final Preferences prefs = Preferences.userNodeForPackage(RoadNetworkConstants.class);
  		if (prefs != null) {
  			if (type == null) {
  				prefs.remove("ROAD_TYPE"); //$NON-NLS-1$
  			} else {
  				prefs.put("ROAD_TYPE", type.name()); //$NON-NLS-1$
  			}
  		}
  	}
docs: Set the preferred type of road segment.
  
  @param type is the preferred type of road segment.