imported>Brian Hawthorn: /* top */added the numbers of the two units

2025-10-31T11:39:58Z

top: added the numbers of the two units

New page

{{Short description|Experimental British electric railcar}}
{{Use dmy dates|date=November 2016}}
{{Use British English|date=November 2016}}
{{Infobox train
| background = #006600
| name = Southern Railway 4-DD
| image = Class 4DD no 4902 at Ashford Steam Centre.jpg
| caption = Class 4DD no 4902 in 1972
| interiorimage =
| interiorcaption =
| service = 1949–1971
| manufacturer =
| factory =
| family =
| replaced =
| yearconstruction = 1949
| yearservice =
| refurbishment =
| yearscrapped =
| numberconstruction=
| numberbuilt = 2 sets (8 cars)
| numberservice =
| numberpreserved = 2 DMBTs
| numberscrapped = 2 DMBTs, all TTs
| formation = {{abbr|DMBT|Driving Motor Brake Third}}-{{abbr|TT|Trailer Third}}-TT-DMBT
| fleetnumbers = 4001-4002
| capacity = 552 seated, 150 standing (per set)
| operator = [[British Rail]]
| depots =
| lines = Charing Cross to Dartford
| carbody =
| trainlength = {{convert|257|ft|5|in|m|2|abbr=on}}
| carlength =
| width = {{convert|9|ft|3|in|m|2|abbr=on}}
| height =
| floorheight =
| platformheight =
| entrylevelorstep =
| art-sections =
| doors =
| maxspeed =
| weight = {{long ton|133|0}}
| acceleration =
| deceleration =
| traction = [[English Electric]]
| engine =
| poweroutput =
| transmission =
| aux =
| powersupply =
| hvac =
| electricsystem = 750 V DC
| collectionmethod = [[Third rail]]
| uicclass =
| aarwheels =
| bogies =
| brakes = Electro-pneumatic
| safety =
| coupling = Screw-link
| multipleworking =
| gauge = {{RailGauge|ussg}}
}}

The '''SR Class 4DD''' was an experimental [[Bilevel rail car|double-decker]] [[electric multiple unit]] built in 1949 and operated by the [[Southern Region of British Railways]] until 1971. Conceived by [[Oliver Bulleid]] for the Southern Railway's commuter line from [[Charing Cross railway station|London Charing Cross]] to [[Dartford railway station|Dartford]], the two trains were the only double-decker trains to be used on the mainline railway network in Britain. Whilst commonly used in continental Europe and North America, the restrictive railway [[loading gauge]] in the United Kingdom prohibits normal double-decker trains with two fully separated decks.

==History==
The 4DD was more split-level than truly double-deck because the compartments were alternately high and low to ensure that the overall height of the train was exactly within the [[Engineering tolerance|clearances]] necessary to safely pass through tunnels and under bridges. A mock-up was displayed at [[Marylebone station|London Marylebone]] in 1949 shortly before it was first introduced into service,<ref>Archived at [https://ghostarchive.org/varchive/youtube/20211205/1a2K0TP1lxM Ghostarchive]{{cbignore}} and the [https://web.archive.org/web/20140419235335/http://www.youtube.com/watch?v=1a2K0TP1lxM&gl=US&hl=en Wayback Machine]{{cbignore}}: {{cite news| url = https://youtube.com/watch?v=1a2K0TP1lxM| title = Double-Deck Train (1949) | via=[[YouTube]]|work=[[Pathé News|Associated British-Pathé/RKO-Pathé]]}}{{cbignore}}</ref> but an assessment after one year in service revealed that the design would not be the optimum solution to the problems of overcrowding, nor would it help increase capacity, and the decision was made to extend trains from eight coaches to ten coaches by using regular, single-decker [[multiple unit]]s.<ref name=world>{{cite magazine| title = Double-decker to go| department = News of the month| magazine = Railway World| location = Shepperton| publisher = Ian Allan| publication-date = November 1971| volume = 32| issue = 378| page = 467}}</ref>

[[File:SR Class 4DD Model.jpg|thumb|A model of the SR Class 4DD]]

The intention to carry more passengers in a train of the same length as other contemporary stock was met, with the two 4-DD units having 1,104 seats compared to 800 in other units of similar age. However it was found that the additional number of passengers meant longer time spent at stations to allow passengers to get on and off.<ref name=world /> In practice, the upper compartments were cramped and poorly ventilated because the upper-level windows were impossible to open due to tight clearance. To resolve this problem, the compartments were pressure-ventilated, but the equipment proved to be unreliable.

Near the end, they were renumbered 4901 and 4902. 4001 and 4002 were reassigned to another pair of prototype Southern Region four-coach EMUs, the [[British Rail Classes 445 and 446|4-PEPs]].

Unusually for an "experiment" they lasted in traffic from 1949 to 1971, undergoing [[Planned maintenance|routine maintenance]] and repaints with no hiccups in their life. The two units were finally withdrawn on 1 October 1971 having travelled approximately 700,000 miles in service.<ref name=world />

==Formations==
{| class="wikitable"
!Key:
|bgcolor=lightgrey |Scrapped
|bgcolor=lightskyblue |Preserved
|}

{| class="wikitable"
!colspan=2| Unit Numbers !!rowspan=2| {{abbr|DMBT|Driving Motor Brake Third}} || rowspan=2|{{abbr|TT|Trailer Third}} ||rowspan=2| TT ||rowspan=2| DMBT || rowspan=2|Notes
|-
!Initial<br>number!!Final<br>Number
|-
| 4001||4901 || bgcolor=lightgrey|13001 || bgcolor=lightgrey|13501 || bgcolor=lightgrey|13502 || bgcolor=lightgrey|13002 || (built September 1949)
|-
| 4002||4902 || bgcolor=lightskyblue|13003 || bgcolor=lightgrey|13503 || bgcolor=lightgrey|13504 || bgcolor=lightskyblue|13004 || (built October 1949)
|}

==Preservation==
Driving motor cars 13003 and 13004 survive, the former at Kent Locomotives Ltd - Sellindge, Kent,<ref name=VCT13003>{{cite web |url=http://www.cs.rhrp.org.uk/se/CarriageInfo.asp?Ref=555 |archive-url=https://web.archive.org/web/20211027071945/http://www.cs.rhrp.org.uk/se/CarriageInfo.asp?Ref=555 |url-status=dead |archive-date=27 October 2021 |title=SR 13003 4-DD 'Double Decker' Driving Motor Brake Third built 1949 |publisher=Vintage Carriages Trust |access-date=1 November 2017}}</ref> and the latter at the [[Northamptonshire Ironstone Railway Trust]].<ref name=VCT13004>{{cite web |url=http://www.cs.rhrp.org.uk/se/CarriageInfo.asp?Ref=556 |archive-url=https://web.archive.org/web/20211027061753/http://www.cs.rhrp.org.uk/se/CarriageInfo.asp?Ref=556 |url-status=dead |archive-date=27 October 2021 |title=SR 13004 4-DD 'Double Decker' Driving Motor Brake Third built 1949 |publisher=Vintage Carriages Trust |access-date=1 November 2017}}</ref> 13004 was moved to Kent by the Bulleid 4DD group to join 13003 in May 2023. One trailer was also preserved, but it was scrapped when [[Ashford Steam Centre]] closed in 1984, in lieu of rent owed.<ref name=SR457>{{cite magazine |title='O1' saviour Esmond Lewis-Evans dies |first=Thomas |last=Bright |magazine=Steam Railway |issue=457 |page=18 |publisher=Bauer Consumer Media |location=Peterborough |date=3 November 2017 |issn=0143-7232}}</ref> Driving motor cars 13003 and 13004 are now (May 2023) both in the care of Bulleid 4-DD Group, which is restoring one of them.<ref name=VCT13003/><ref>{{Cite news |last= Hepworth|first=Tom|date=28 September 2025 |title=How Oliver Bulleid helped shape modern Southern rail |url=https://www.bbc.com/news/articles/cwyrwy0vrryo |access-date=2 October 2025|publisher=BBC News}}</ref>

==References==
{{Reflist}}
{{Marsden-SouthernEMU1|pages=85–88}}

==Further reading==
*{{cite magazine|title=Cash plea for Double-Decker EMU's 50th birthday rebuild|magazine=[[Rail (magazine)|Rail]]|issue=345|publisher=EMAP Apex Publications|date=2–15 December 1998|page=63|issn=0953-4563|oclc=49953699}}

==External links==
* [http://members.tripod.com/~dart75/bdds.htm Bulleid Double Decker Society]
* [https://www.britishpathe.com/asset/82675/ 1949 British Pathe newsreel footage of the pre-production mockup]
* [https://www.britishpathe.com/asset/72687/ British Pathe newsreel footage of first day of passenger service]
{{British Rail EMU}}

[[Category:Southern Railway (UK) electric multiple units|4DD]]
[[Category:British Rail electric multiple units|SR 4DD]]
[[Category:Train-related introductions in 1949]]
[[Category:Double-decker EMUs]]
[[Category:750 V DC multiple units]]

SR Class 4DD - Revision history

imported>Brian Hawthorn: /* top */added the numbers of the two units