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Bulleid 4DD class

A post-war resurgence in passenger traffic on suburban services to and from Dartford had led to overcrowding. Extending train length was not an option at the time due to the need also to extend platform lengths and make other related infrastructure improvements. Shortly before the railways were nationalised in 1948 a typically bold and innovative solution emerged from Oliver Bulleid and the Southern's carriage works at Eastleigh for a double decked EMU design. Unlike the double decked commuter cars already in use in the USA which were of a spacious open "gallery" design the restrictive British loading gauge forced a far more cramped solution. The way to achieve two levels was to interleave upper and lower level compartments along the length of a car, the upper level compartments being reached by a short flight of steps from a neighbouring lower compartment. Two experimental four car units numbered 4001 and 4002 were constructed. Construction was similar to their contemporary Sub units but forerunning the EPB units to follow were fitted with Westinghouse non self lapping electro-pneumatic brakes and roller blind headcode boxes. Other "firsts" were installation of strip lighting and pressure-air ventilation, but these were of necessity forced by low ceiling heights and non opening windows on the upper level (the latter for safety reasons since the cars were built to the limit of the loading gauge). Footboards to passenger accommodation were not fitted as this would have resulted in the units beyond the loading gauge. Whilst the motor bogies were modifications of the standard Southern 8'9" bogie with 3'2" diameter wheels the trailer bogies had 8' frames with 3' diameter wheels. The original wheels were of a welded BFB type but these caused problems and were they replaced with wheels of a more conventional construction.
 
4001 before the days of yellow warning panels. The location is thought to be Slades Green (before it became just Slade Green).

photograph: Glen Wood collection

4001
 
4001 4001 again, with warning panel but before the days of all-yellow ends. Note the more modern number blind when compared with the photograph above.

photograph: Glen Wood collection

 
Construction was at Lancing works in 1949, the first set emerging in September and the second in October. Due to operating restrictions the two units usually worked together as an eight car unit and they were confined to the Dartford routes. The experiment was not a success as they were unpopular with both the operators and passengers. Each unit seated 508, 122 more than the equivalent late series 4 Sub unit. Driving cars had five upper and lower compartments accommodating 55 passengers on each level. The trailer cars seated 66 on the high level within six compartments and on the lower 78 within seven compartments. Also on the high level were tip up seats positioned under the large middle window. The passenger accommodation was cramped and despite the pressure air ventilation the upper levels became uncomfortably hot during warm weather. Also passenger loading and unloading time was extended with 36% more passengers needing to use the same number of doors as a single level unit. Construction costs were also 50% greater than comparable single level units due in part to the need to construct from new rather than re-use underframes and bogies (as was the Southern's custom). Thus the experiment did not lead to more double deck units, with the result being the need to upgrade the infrastructure and run ten car trains, although the two units survived plying commuters between Dartford and the London termini until the autumn of 1971. In their latter days they carried BR overall blue livery and were renumbered 4901/2. The last service they worked was between Charing Cross and Dartford via Bexley on the 1st October 1971. They were then withdrawn and sold for scrap. Two motor coaches from these historic units survive. One is Hope Farm, Sellindge (near Ashford) - where Southern Locos used to be based, the other (DMBS 13004 from set 4002) is currently being restored at the Northampton Ironstone Railway. Bulleid Double Decker Society
 
4002, the second of the '4DD' class double-deckers, is pictured as the leading unit entering Charing Cross in June 1970.

photograph by Michael Taylor

4002
 
4001 4001, the first of the DDs will be the leading unit when it leaves on its next working out of Charing Cross in June 1970. Note both units are still in green at this time although they will eventually succumb to overall BR blue for their final days.

photograph by Michael Taylor

 
Ironically, in 1999 overcrowding on another part of the Southern - this time commuter services into Waterloo - led to the proposal by South West Trains to introduce double decked trains! If these plans go ahead it will be interesting to see if the current railway management, many of whom do not have a background in railways, will learn from the lessons of the past.
 
This plaque is at Dartford railway station, commemorating the 4DDs on the route where they spent their working lives.

photograph by Bob Boyd

Plaque

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This page was last updated 19 May 2010

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