SR Class 4DD
As a class, 4 DD the two electric railcars compositions are known which could make the Southern Railway, and in 1949, 4001 4002 taken by the British Railways with the numbers. The vehicles were designed by Oliver Bulleid and owned as a special nested compartments persons. The vehicles were placed out of service in 1971. Two railcars - but not the associated passenger cars - are still preserved.
The Southern Railway had to Dartford after the Second World War through the passenger growth a space problem in the commuter trains. The eight-car EMUs (Class 405) were overcrowded regularly. However, since the length of the platform was limited, they tried to solve the problem with increasing the capacity. However, since the narrow English gauge does not allow double-decker cars, had to be resorted to a trick in order to offer more seats for the same train length can. This was achieved by using a higher compartment was placed between two compartments with English door assembly. This was achieved a 50 % higher number of seats than normal, single-story arrangement. One sat in the elevated compartment above the seats of the underlying compartment. Access to the compartment was increased by a staircase from an underlying compartment. The windows of the upper compartment but had to be carried out firmly for safety reasons and were provided with a forced ventilation. This ventilation but it did not reach a satisfactory air and there was therefore also always complaints. Also, the service life increased on the platform by 38 %, as compared to the one-story version had to use up to twice the number of people a single door. The vehicles were larger than the control gauge and they could not therefore be used freely. Therefore, it remains at these two compositions and instead had to be procured prolonged, one-story train compositions (Class 415/6 ), which were extended by a car, so you could make ten -car compositions.
The railcars were indeed in multiple unit control can also operate with other one-story railcars, but due to operational constraints it wrong usually together as 8 -car composition, and this only on the routes to Dartford.
Two railcars formed with two cars, a four -piece unit, although only the railcar on one side had a cab, and thus had to rely on a second railcar. The railcars were next to a multi-function compartment ( luggage and passengers), 5 lower and upper compartments 4, the passenger cars 7 lower and upper compartments 6. A half train thus offered 508 seats. They were, however, very closely, you went but from an occupancy of up to 11 people in a compartment of normal.
The lower parts of the vehicle were similar to the previous train set, only smaller wheels fitted (3 ' instead of 3'2 '' ), but not the long carrier between the bogies were lowered. The electrical equipment was under-floor mounted.
The cars had the lower deck, a floor height of 1121 mm above rail level. This height can be explained partly by the high Peron.