2011 Headway calculation

[PJW]

1. Whereas I would agree with Peter for the assessing of Minimum Reading Distance of a signal for signal sighting purposes that you must use the maximum line speed as the worst case, when assessing for headway considerations whether the driver of the 2nd train would see a cautionary aspect. then the headway speed is the one to use. However the 10sec is itself a somewhat arbitrary figure and the difference in the distance calculated at the two speeds is unlikely to be very significant.

4. You should read the wording of the question very carefully as it does subtly change from year to year. Sometimes the wording is such that it should be evident that they do NOT want you to make any contingency allowance at all and therefore it would be wrong to include.

Be aware that the examiners are trying to check whether you really have a full understanding rather than just be able to reproduce a learned methodology, so I recommend that you focus your study on developing this generic comprehension rather than worry unduly about particular points of detail for any particular year's question.

1. For UK applications, a 10 sec sighting time is an established norm. It should be at line speed as this is the worst case for a train approaching the signal. You will see a typical of 200m in some examples, but this a simplistic generalisation.

4. Contingency is a value judgement...
Peter