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A slam-door train or slammer is a set of diesel multiple units (DMUs) or electric multiple units (EMUs) that were designed before the use of automatic doors on railway carriages was common. The name came about because of the characteristic noise passengers slamming the doors made when the train was about to depart.
Some slam-door train designs featured doors that could only be opened from the outside, so it was common for passengers to lean out of the window to reach the outside door handle.
Slam-door trains had many more doors than newer trains (which tend to have only two sets of doors per coach); some designs featured a door for every individual seating bay. Some units had individual compartments, each with its own door and no access to any other part of the train; however, these were unpopular due to security concerns and the lack of access to toilets for longer journeys and many were later converted to standard corridor saloon design.
The term "slam-door" could also refer to locomotive-hauled railway coaches that did not have automatic doors, but this usage is less common. The term "slam-door train" generally applies to BR Mark 1 EMUs and DMUs.
Slam-door EMU and DMU trains were commonplace ever since the introduction of electrification. While there were early examples of the type, which are beyond the scope of this example, they became commonplace on the Southern Railway in the 1930s when it electrified its main routes around the South of London at 750 VDC (third rail), in particular, the line to Brighton.
Slam-door diesel multiple units became common in the 1950s when British Railways (BR) sought to modernise its network and do away with steam locomotives. Many one, two and three coach units were built for non-electrified lines all around the country, in particular, these were popular on branch lines where it was uneconomic to electrify. These units were later classified in the Class 101 – 129 series, dependent on the design.
Meanwhile, large new fleets of electric slam-door trains were being built for use around the country. AC units were built for the newly electrified routes to Southend-on-Sea, Colchester and Clacton; also for some routes around Manchester. These AC units were later classified as British Rail Class 302 through to British Rail Class 312, again dependent on the design. AC units for Glasgow, however (classes 303 and 311) had power operated sliding doors.
In the Southern region, the early units were replaced in the 1950s and 60s with new slam-door third-rail electric units, first of all the compartment commuter units '4-SUB' and '4-EPB' (BR Class 415) and later the much more comfortable longer distance trains which survived in use until the early years of the 21st century. These included the '4-CIG' British Rail Class 421), '4-CEP' (British Rail Class 411) and '4-VEP' (British Rail Class 423); the former two being fairly similar while the latter was designed with more crowded seats and more doors to enable faster unloading and loading of passengers.
Finally, also on the Southern division of British Rail, new slam-door diesel multiple units were introduced in the late 1950s, these were classified as British Rail Class 201 and similar and were affectionately named 'Thumpers' due to the distinctive noise they made.
The slam-door trains have had a long and robust service life, but have gradually been replaced by newer units with automatic doors. These newer units are safer as the doors are locked centrally. This facility, via a form of central locking has now been fitted to surviving public rail line units. In the past, slam-door trains' doors could be opened at any time, even while the train was moving.
The introduction of the British Rail Class 313 AC EMUs and later derivatives of this class in the late 1970s and early 1980s saw the beginning of the end for the AC slam door trains. The very similar British Rail Class 455 trains around London displaced the 4-EPBs while introduction of the '5-WES' (British Rail Class 442) 'Wessex Electrics' in 1988 and electrification of the line to Weymouth saw the end of yet more slam-door trains.
At the same time, BR had introduced a new type of DMU, the British Rail Class 150 'Sprinter', which competed with slam-door DMUs.
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 Bombardier Voyager and Turbostar DMUs and Electrostar and Siemens Desiro and Pendolino EMUs. However, many InterCity125 slam-door trains still remain in use, but are due to be withdrawn in the next 10 years.
Due to a number of high-profile accidents in the 1990s, the manually-locked slam doors were supplemented with electronic, driver-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 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' (British Rail 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' (British Rail 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.
One British Rail Class 121 "Bubblecar" single coach DMU was still in use on the mainline railway network until 19th May 2017. This was on the Aylesbury to Princes Risborough line, and only operated at peak times.
Another problem is that many units 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.