A couple of months ago I noticed new A2 route markers at various points on Old Windsor Road (and M2 markers on some of the signs on the Hills Motorway), replacing the hexagonal Metroad 2 markers.
A2 route marker at the intersection of Norwest Blvd and Old Windsor Rd
The new alphanumeric numbering system replaces the existing mixture of Metroad, State and National route markers in NSW. It’s based on the British system where the letter denotes the road category and the number designates the route. Interestingly, this means that both the Sydney–Newcastle “F3” Freeway and Southern “F6” Freeway will be designated M1.
The Westlink Motorway was the first major length of road in NSW to use the new system when it opened in 2005, being signposted with M7 alphanumeric markers, but the rest of Metroad 7 retains the previous designation for now.
M7 route marker on Norwest Blvd (note the Metroad 2 marker in the background)
According to Ozroads, the transition to alphanumeric route numbering in NSW has been underway since 2004 – particularly in rural areas – with other states (except WA) mostly in more advanced stages of transition. I think that the new road numbering system is great because it provides more road information to drivers, while reducing potential confusion through rationalisation and national standardisation of route markers.
Update (May 2014): Statewide implementation of alphanumeric route numbers was completed during 2013 (along with further rationalisation and renumbering of routes). To avoid potential confusion with M1, the Sydney–Newcastle Freeway and Southern Freeway were renamed Pacific Motorway and Princes Motorway respectively.