of stored locomotives, now up to 50 years old. Passenger Early passenger services were operated with 4 and 6 wheeled "dogbox" passenger carriage with small compartments and no side corridors. Later years saw the provision of side corridors to provide access down the train, and onboard toilets. Sleeping carriages was first introduced in 1887, and dining cars from 1908. Larger bogie rollingstock started to appear from the turn of the 20th century, with the E type carriage stock introduced on The Overland, and smaller W type carriage stock on intrastate trains. The first air conditioned carriage was introduced in 1935, when one of the E type carriages was fitted. All steel carriages came to the Victorian Railways in 1927, with the construction of the "Avoca" and "Hopkins" dining cars, followed by the S type carriage stock for the new Spirit of Progress in 1937. On the Melbourne suburban network, Electric Multiple Units were introduced speeding up services. Experiments were also made with various diesel and petrol railcars for use smaller branch lines, with the DERM being the most successful, remaining in service from 1928 to 1991. A fleet of Walker railcars was also introduced in the 1950s, along with Z type saloon carriage stock for both intra and interstate trains. By the 1980s, country passenger services were run down, and older wooden rolling stock was now approaching their use by date. As a result, the N type carriages were introduced from 1981, followed by the converted H type stock from 1984. Since then, diesel multiple units have become the norm for new purchases, with the Sprinter introduced in 1992, and the VLocity from 2005. Freight Early wagons were of all-wood construction, followed by wooden bodies on steel underframes, then all-steel wagons. They were built on four-wheeled underframes, but in 1871 bogie vehicles began to appear. Groups of wagons of the same design are classed together by a multiple character alphabetical code, initially in a system restricted to Victoria only, but from 1979, the Railways of Australia four letter coding was introduced. Under this system, the first letter represents the owner of the wagon, the second represents the general type of wagon, the third separates different classes of the same general type, and the fourth letter indicates the maximum running speed. The last four-wheeled open wagons were built in 1958, but were not scrapped in large numbers until the 1980s, when