the Automatic Block System (ABS) of safeworking, where the presence of trains automatically control the signals after them, providing a safe distance between trains. Introduced from 1915, the system was based on American speed signalling practice with GRS2A upper quadrant mechanical signals with two arms able to indicate up to 5 different speed aspects to train drivers. These signals were later replaced by colour light signals which are the standard today, but the old mechanical style remained until 2001. A variant of the Automatic Block System, Automatic and Track Control (ATC) has since been introduced, which provides the same benefits as ABS on single lines of track, while still ensuring only one train in a section at a time. Centralised Traffic Control was also introduced in the 1960s on the new standard gauge line to Albury, and then on the main interstate line to Adelaide, allowing trains to be directed from a distance. Today, little mechanical signalling remains, with local signal boxes controlling signals abolished from many areas as part of the Regional Fast Rail project. The suburban network and busier regional lines use variants of Automatic Block Signalling, while quieter lines use the Train Staff and Ticket or Train Order systems of safeworking. Train protection has also progressed, with the Train Protection & Warning System also introduced on major passenger lines as part of the Regional Fast Rail project. Rollingstock Rollingstock in Victoria has used air braking since tests of continuous train brakes were carried out in 1884. Initially, screw couplings were used to connect wagons, but from 1924, automatic knuckle couplers were introduced, with buffers removed from freight wagons by 1960. Locomotives In Victoria, groups of locomotives of the same design are classed together by letter, in a system introduced in 1886. Initially, low letters were given to passenger classes, and high letters for goods classes, but from about 1916, this pattern was discarded. Within classes locomotives are individually numbered, in a continuous number block which is unique to the class. In some cases, locomotives have been renumbered to keep number blocks continuous, and in some cases there is no correlation between the number blocks used for the steam and diesel locomotives of the same class letter. In addition, some classes start the number series with a 0, while others start with a 1. The first locomotives used in the state were small steam locomotives, and by the