What is "ATO"? Jun 14, 2012 17:23:51 GMT
Post by bananaman on Jun 14, 2012 17:23:51 GMT
The loops are just a side effect of how the other systems work - they communicate by using the loop as antenna to transmit "codes", whereas on the Central Line the codes are sent through the track.
This isn't related to the Central Line's ATO not stopping in the correct place, which only generally happens in adverse weather. Someone more knowledgeable than me will know exactly why this happens
One cause of trains stopping short (on the Central) is wheel slide. If the train detects that the wheels are sliding, in wet or greasy conditions for example, it will apply the brakes. When this happens it can "forget" exactly where it is.
The Central Line does use loops on the track, but they are not continuous like the Jubilee and Northern systems, and they are used for different purposes. There is a loop at the approach end of the platform which reminds the train of the distance to the stopping marker. Where the front end of the train stops there are another two loops which communicate with the train (one transmits, one receives). These loops are referred to as ATO loops.
On points and crossing tracks it is impractical to transmit codes to the train via the rails, so this is done via cable loops. These are referred to as ATP loops (ATP means automatic train protection). Finally, at various locations along the track there are Spot loops, which tell the train how to interpret the codes received from the rails. These are not to be confused with the Victoria line spot loops which did a different job.