"Route Numbering". Guidelines for Direction Signs in the Perth Metropolitan Area. Main Roads Western Australia. 21 September 2011. Archived from the original on 21 October 2013. Retrieved 17 November 2013. Main Roads has chosen to retain the shield numbering system
"Route Numbering". Guidelines for Direction Signs in the Perth Metropolitan Area. Main Roads Western Australia. 21 September 2011. Archived from the original on 21 October 2013. Retrieved 17 November 2013. Main Roads has chosen to retain the shield numbering system