e-TAG is an electronic toll collection system used on all tollways throughout Australia. Based upon the DSRC protocol, it was originally developed by Transurban for use on their CityLink tollway in the early 1990s, with the system since adopted by all electronic tolled roads, bridges and tunnels in Australia. There are over 850,000 e-TAG account customers, and over 1 million e-TAGs have been issued. In early 2009, the Sydney Harbour Bridge became toll-booth free, so an eTag must be used for one to cross the bridge. The technology has different names depending on the issuer - such as Breeze (Eastlink Melbourne), Flow (CLEM7), Go Via Queensland), E-toll (Roads and Traffic Authority NSW) and E-way (Sydney motorways M5 and M1), however these are all interchangeable across Australia and no surcharges are charged for use on other operator's tollways.
Australia was one of the first countries in the world to have complete, surcharge-free interoperability between rival tolling providers across different roadway jurisdictions (states).
The e-TAG tolling is based on a modified Identification Friend or Foe system.