it was sometimes re-used; for example, two A classes exist, one from 1873 and one from 1906. Traffic Monitoring System Following the introduction of the computer-based Traffic Monitoring System (TMS) and consequent renumbering, classes were identified by the two upper-case letters with the first letter remaining D or E respectively and sub-classes being indicated by a third upper-case letter, such as DAA (DA modified for hump shunting), DAR (DA with rebuilt superstructure), DFT (DF with turbo-conversion), DXR (rebuilt DX) and so on. Most diesel shunting locomotives have a three-letter classification with DS as the first two letters, following on from the original diesel-hydraulic shunting class that was known simply as the DS class. For electric locomotives the second letter generally referred to where the locomotive was based, such as EC in Christchurch, EO in Otira and EW in Wellington. The EM class in Wellington stands for Electric Motor and the ET stands for Electric Trailer. The DM class units were an exception to this. Most railcars were classified RM (Rail Motor), and individual classes were known by alternate names such as the Vulcan railcars of the South Island and the Wairarapa railcars that ran over the Rimutaka Incline. List of locomotive classes Mainline diesel locomotives Diesel shunting locomotives Electric locomotives Battery electric locomotives Electric multiple units Wellington electric multiple units operate on 1500 V DC overhead. Auckland's electric multiple units run on 25 kV AC overhead. Railcars Livery: The first railcars were painted "carnation red" with a white or yellow stripe. The Silver Fern railcars appeared in stainless steel. All railcars, unless otherwise stated, are designated RM class. Here, they are classified under their common names. Experimental railcars included the following: Diesel multiple units Steam locomotives Livery: New Zealand steam locomotives after the late 1920s were mainly completely black with red buffer beams at each end. Earlier steam locomotives were more varied in colour with polished brasswork and a contrasting lining on the cab sides and side tanks, for example the green of the F class Peveril. Steam locomotive notes: Two other types of locomotives built in the 1870s were included in the A class. All three had a wheel arrangement of 0-4-0T, but were technically and aesthetically quite different. The other A types are often known as the Shanks A and the Mills A, after their respective builders. A completely different type of locomotive was nominally classified as being