introduced a new type of DMU, the Class 150 Sprinter. The final build of slam-door stock were the Class 312s in the mid-1970s. The development of a new generation of multiple units in the early 2000s enabled the now-privatised train operators to finally replace the slam-door trains (which were over 40 years old in some cases) with modern, new units. These included Alstom Coradia and Bombardier Turbostar DMUs and Bombardier Electrostar and Siemens Desiro EMUs. Due to a number of high-profile accidents in the 1990s, the manually-locked slam doors were supplemented with electronic, driver- or guard-operated central locking before they were gradually phased out in favour of sliding doors through the 2000s, resulting in a sharp decline in the number of deaths per year from passengers falling from trains. The last slam-door stock was withdrawn by South Eastern Trains in December 2005. Single-coach Class 121s were reintroduced by Arriva Trains Wales and Chiltern Railways to operate services from Cardiff Bay to Cardiff Queen Street and Aylesbury to Princes Risborough respectively. These were withdrawn in 2013 and 2017. Preservation The last units were withdrawn from the mainline railway network in November 2005, and South West Trains ran slam-door trains on the Lymington branch line in Hampshire until 22 May 2010. It had taken two '3-CIG' (Class 421) units and installed central locking and ran the service as a 'heritage line'. South West Trains has also retained a complete 4-VEP (Class 423) unit which is in storage. Other examples of slam door trains are held by various museums and private groups, however there are no remaining examples of some types of the units, with the AC electric units having fared particularly badly. Slam-door electric trains are generally unattractive to preserved railways as they are unable to run under their own power while diesel units remain in service on many preserved railways around the UK. Another problem is that many slam-door trains contain asbestos. This was removed from some when they were refurbished in the 1980s, but many slam-door trains were incinerated to destroy the asbestos. Those that remain have to be treated by anyone that wished to purchase them, which is a very expensive process that also damages the units. References Further reading British Rail rolling stock