Correct Side Door Enable
Correct Side Door Enable (CSDE) is installed on London Underground rolling stock and, effectively, does exactly what it says - it 'enables' (or allows) only the doors on the correct side of the train to be opened, in appropriate places.
Why is there the need for CSDE?
As a bit of background, during the days when guards formed part of a train's crew, the guard was responsible for opening the trains doors, which he did from panels located on either side of the train. He had a routine for this: he would open his own door and, when satisfied that the train was stopped correctly, would then open the train doors.
However, with the demise of guards and the introduction of 'One Person Operation' (OPO), it then became part of the Train operator's duties to open and close the doors of the train. Trains were modified so that the doors could be opened from the driver's desk, but the possibility of the Train Operator opening the doors on the wrong side of the train soon became apparent.
Obviously, this is something that carries considerable risk to passengers - if the doors were to be opened on the wrong side there is a chance that passengers, particularly if they are leaning against a door, could fall from the train. The dangers attached to this are several. There is the risk of electrocution, should the victim come into contact with a current rail and, in sections where there are adjacent tracks, it would be possible for the victim (or victims of course - several people may have fallen out) could be hit by a train arriving in the opposite direction.
Additionally, there is the possibility of the doors being opened between stations, with the same results as described previously.
When OPO was first introduced, there were a number of instances where the doors were opened incorrectly, and it was quickly realised that measures needed to be taken to prevent this. Initially some stocks were equipped with a switch which the Train Operator had to select to allow the doors to be opened on the correct side. Although this was an improvement, it did not solve the problem entirely, so a more 'fail safe' system was needed.
The solution was Correct Side Door Enable.
How does CSDE work?
There are a number of elements involved in CSDE, and, if they all come together as planned, it will only permit the train's doors to be opened both on the correct side of the train, and if the train is stopped in the correct place.
Platforms are equipped with a 'loop' that acts as a transmitter to the train borne equipment. This in turn is activated by a switch from the platform which can be cut out (turned off) should the station be closed, or a platform unavailable for use - perhaps for refurbishment. If the circuit on the platform is cut out, this would result in no signal being sent to the train and this would prevent the doors being opened normally. There is an override facility on the trains, but this will be explained more later in this article.
In the photo above, it is possible to see the platform loop installed below the platform edge. As can be seen, the loop is quite long at this location and allows quite a considerable tolerance in the stopping position of the train. Not all loops are this generous.
This illustrates the CSDE control switch and it's associated box of equipment. All platforms are equipped with such equipment.
There are two elements to this - the external equipment and that fitted in the cab. The first element of the equipment is the receiver on the train that senses the signal and enables the doors to be opened.
The receivers are located externally on both sides of the train, close to the front of the train and just below the driver's cab. The exact locations vary from stock to stock, as can be seen from the images below.
This is the receiver on a C Stock unit - it is the probe like device attached on a plate to the step which allows access to the cab. You can see the probe is located almost at the very front of the unit.
This is a similar device fitted to a D Stock unit.
Alternative view of the D Stock CSDE receiver
To try to put the preceding two images into context, this image is looking at a D Stock train from in front of the train. The step and the CSDE receiver can be seen below the light cluster. The receiver is actually located about four feet from the front of the cab
Having dealt with the external equipment, we move to the cab equipment. Again, the C and D Stocks carry the same equipment, but it is located in different positions in the train's cab.
There are only two elements which involve the Train operator - the Door Enable Zone lamp illuminates when the train is stopped in the correct position, providing the platform borne equipment is functioning correctly. This is an example of a D Stock, where the panel is located on the Number 2 Auxiliary panel, an example of which can be seen here.
The same equipment, but fitted to a C Stock. The only difference is that this time it is located on the rear bulkhead (see here for a wider view) and the zone enable lamp is shielded, though it is clearly visible from the driving position. Note too the warning about the use of the override device; further mention of this will be made later. The reference to the Contactor Box is for the benefit of maintenance staff - the Train Operator has no dealings with this.
So, that has effectively covered the equipment that is involved in the operation of the CSDE. But what happens if the driver has missed the loop, or there is a fault with either the train or platform equipment. How does the Train Operator open the doors?
This is where the Door Enable Override button comes into the equation, but - as suggested above - this must be used with great care, as once operated, the doors on both sides of the train can now be opened. So there is a very rigid procedure which must be followed should this equipment need to be used.
The procedure goes as follows:
The Train Operator will firstly ensure that the station is indeed open - this should be easily confirmed, either by the presence of passengers on the platform or, alternatively, 'Station Closed' boards should be displayed, if it is not open.
The Train Operator then operates the Door Enable Override plunger.
The Train Operator then opens his cab door on the side of the train where the platform is located, and confirms this by putting one foot onto the platform. This is to overcome the possibility of opening the doors on the wrong side of the train.
Using the Door Open buttons on the rear bulkhead, the train doors will then be opened. The buttons on the driver's desk must not be used. In fact C Stock trains have been further modified so that if the CSDE Override is operated, the door open buttons on the driver's desk are disabled.
Although that sounds quite involved, it can all be achieved in just a few seconds, and done in perfect safety, provided that all the steps have been correctly observed.
Of course, no procedure is absolutely infallible, particularly where there's a 'human element' involved. But, as with every such process the aim is to make the risk 'As Low As Reasonably Practical' or 'ALARP' as it's known. So should there still be a wrong side door opening there is a whole set of procedures that then come into operation to address that eventuality.