Central Door Locking (CDL)

This article was opened on 10 January 2005, and
last modified on 25 February 2024.

The section on On-train Monitoring Recorders has been moved to its own page.

[PHOTO: external release-cock on train bodyside: 22kB]

Any system which locks doors needs to have an emergency override. These views show the completed systems. Above: One external release-cock is located on each bodyside, just above solebar-height. Below: The internal override system in the vestibule at each doorway.

[PHOTO: internal release handle: 39kB]

Current fleet status of CDL (as at 24 April 2023)

Number / name Vehicle type Progress
60118 Tunbridge Wells Motor Coach Completed 6 April 2007, certified 22 June 2007
60116 Mountfield Motor Coach Completed 3rd week May 2007, certified 22 June 2007
60529 Trailer Completed, certified 3 June 2008
60501 Trailer Completed, certified 3 June 2008
69337 ex-BIG Buffet-car Completed, certified 23 June 2008
70262 CEP trailer Completed, certified 16 March 2010
60528 Trailer Completed, certified 24 April 2023
60119 Motor Coach Completed, certified 24 April 2023
60000 Motor coach Work well progressed
60502 Trailer Work begun

On Friday 22 June 2007 the two Motor Coaches described at the top of the table above passed inspection and, given the completion of a parallel project to fit OTMR, were re-certified to run on the main line. Two trailers and the BIG buffet-car were signed off during June 2008, in time for the train’s first CDL-equipped outing.


[PHOTO: 1001’s cab interior showing final CDL and OTMR fittings: 44kB]

For our trains to run in passenger service on the main line after 31 December 2005, they would need to be fitted with Central Door Locking, a system that prevents passenger doors from being opened except when they are released by the traincrew.

Whilst our train was out of traffic in 2006 for the fitting of CDL, regulations required that before our train could re-enter service on the main line, its driving vehicles would also have to be fitted with “black boxes” or On-Train Monitoring Recorders.

Photo: The finished product! The cab of Motor Coach 60118 Tunbridge Wells, showing the CDL control-buttons on the desk-top and the driver’s OTMR (orange) interface-box at top right. As this article will demonstrate, there is much more to this project than just what can normally be seen in the cab! Photo by Andy Armitage.


To prevent passenger doors being opened except when released by the traincrew, we were required to fit Central Door Locking; unlike the system installed on the 125 High Speed Train, the apparatus we are working with is unobtrusive: it is situated in the same area as the existing door-catch.

Hastings Diesels Ltd began installation work as a prototype for all remaining DEMU vehicles; in view of the length of time typically taken for engineering approval and acceptance to take place, we began on vehicles 60528 and 60019 for this test-bed. These two vehicles were not in railway use as yet as each has been undergoing restoration (see link to each).

The plan was to use these coaches instead of ones from the active unit 1001, to avoid the latter being out of traffic for a long period of time. Unfortunately, fitting CDL has proved to be far from trivial, and the job has been frustrated by several factors:

[PHOTO: Exterior of carriage with indicator lamps: 46kB]

The exterior indicator lamps as seen on 60019 which is seen painted in undercoat. The main lamp lights when doors are unlocked or open, and a smaller lamp next to each door is lit when the local door is unlocked. See also a photo below showing the finished part on test. Photo by Mike Grant.

[PHOTO: Driving-cab interior, fitted with controls for CDL: 61kB]

Above and below: In the driver’s cab, twin red “door release” buttons for both left and right sides are visible mounted on top of the instrument desk; a doors locked visual (or pilot light) is mounted within the desk, between duplex gauge and brake cylinder gauge. Photo by Mike Grant.

[PHOTO: close-up of driver’s desk: 65kB]

[PHOTO: close-up of guard’s control panel: 15kB]

Above: The bell switches in the Guard’s vans now incorporate a blue button which, when operated, will lock the doors throughout the train and illuminate to show that the doors have all locked. The Guard will then operate the bell switch as usual, to ring the signal bell in the driver’s cab.

[PHOTO: Central Door Locking control-unit: 53kB]

Each vehicle requires a Control Unit. After a lot of investigation it was decided that the only suitable space for it would be in the roof-space above the vestibule. This is an upward-looking view, with the ceiling panels removed.

The first CDL control unit was fitted into the ceiling void above the rear vestibule of motor-coach 60019 on 18 June 2005.

[PHOTO: interior view of train door with modifications: 50kB]

Above: This view shows the extensive modification work needed to fit the new door locks on each door. Emergency Release handles will also be added (see photos at top of page); accomodating these has proved to be a design challenge because of the limited space, and wooden boxes have been specially fabricated to blend in with the existing panelling.

[PHOTO: train floor with hatch removed, wiring exposed; 70kB]

Above: A floor-hatch in the saloon of motor coach 60000 Hastings is removed to reveal wiring-connections for the Central Door Locking.

[PHOTO: train bodyside showing lamp illuminated: 18kB]

Above: The completed external door-indicator lamp illuminated on test prior to certification. See also an above photo.

[PHOTO: CEP-coach undergoing work in depot: 83kB]

Above: At the end of October 2009 Trailer Second Open number 70262, better known as our ex-4CEP coach, was having the external door-release and indicators fitted as can be seen. Photo by Andy Armitage.

The completed apparatus, September 2007

These views show the completed CDL works on motor coach 60116 Mountfield.

[PHOTO: instructions and indicator-lamp in vestibule: 52kB]

Above: The instructions and indicator-lamp in the vestibule.

[PHOTO: internal door-handle: 45kB]

Above: The internal door-handle, with the CDL mechanism visible beneath it.

[PHOTO: locking mechanism in doorframe: 34kB]

Above: The double-height striking-plate mounted within the doorframe. The lower “catch” incorporates the locking-pin operated by the Central Door Locking system.

On-train Monitoring Recorders

The section on On-train Monitoring Recorders has been moved to its own page.