denoting their grade. For example, Western Freeway is M8 until Ballarat and continues beyond as A8 Western Highway. They are not used extensively in the Melbourne metropolitan area where the blue-shield metropolitan route system is retained for most routes. The National Highways were retained, but with the route numbers changed to alphanumeric designations. New South Wales and the Australian Capital Territory introduced the alphanumeric system from early 2013. Before being officially announced, new road signs were fitted with such numbers and then being "coverplated" with the existing route number. However, the new system does not distinguish between the former National Highways and other routes. Alphanumeric routes have also been introduced for many major highways and urban routes in Queensland, although many other roads retain markers from the National Route, National Highway, State and Metroad numbering systems. According to the New South Wales Roads & Maritime Services, the Northern Territory has similarly begun converting their numbered routes to alphanumeric routes, with a "progressive replacement" scheme that sees alphanumeric route markers introduced only when signs are replaced. There are no plans to introduce an alphanumeric route numbering system in Western Australia. Prefix letters In the alphanumeric systems, a letter denoting the route's construction standard and function is prefixed to the route number, creating an alphanumeric route designation. One of six letters may be used: "M" routes are primary traffic routes, called motorways in some states. These are typically dual carriageway, freeway-standard highways, but may also be used for rural roads that are nearly at freeway-standard, or at least are dual carriageways. "A" routes are other primary highways, including urban arterials and interstate or interregional single carriageways. "B" routes are less significant routes, either as an alternative to an "A" or "M" route, or linking smaller population centres to larger regional centres, but without being a major through-route in the region. These are the major road links in areas without "A" routes. "C" routes link smaller settlements and towns to the rest of the major road network. They are used for roads without the significance of an "M", "A", or "B" route, but where numbering would assist navigation. "D'' routes are detour routes for motorways. There are only two of them, D1 and D5 "R" routes are ring routes in South Australia. There is only one route, R1 Germany A stands for Autobahn (motorway), B for Bundesstraße (literally "federal road"). There are also