19-08-2011, 07:12 PM
Yes you are broadly correct; the ambition is not to have permissive passenger working except when it is unavoidable due to the timetable requirement to join two trains together and go forward as one (saves train crew and even more important increases capacity as only utilise the one train path in a congested area).
However historically it was regarded as perfectly acceptable, and in truth there have been very few accidents and incidents because of it. At some places there wouldn't be enough platforms to keep to the rule, one train in one platform. Sometimes, subject to risk assessment, it is possible to argue for the perpetuation of permissive moves at a particular site. Other places have got mid-platform signals- I think of Manchester Piccadilly through platforms on the line to Oxford Road and Birmingham New Street. Such places do tend to have very short overlaps, in the range 20m to 50m; even so rather better than the tail lamp of the previous train that has a zero overlap.
In some places (pretty sure The Netherlands is one) the platform staff wheel out on the platform a portable stop marker signal that if battery fed from the platform trolley on which it is mounted- this tells the incoming train driver exactly where to stop (and thus choose an appropriate overlap for the circumstances) and once it has served its purpose they wheel it away again.
I don't know the history of the BTM mid platform markers (i.e. whether they pre-date the current signalling that I believe dates from the late 1960s/ early 1970s); not sure they are actually unique, but cannot think of an equivalent elsewhere. Not in the Rule Book but I guess in some local operating instructions; very Western Region- cheap and simple and serves the purpose, so can't see it being adopted as a national standard.
As Peter said, there is less concern about terminal platforms particularly if the approach visibility is good. It is all about controlling risk and balancing any theoretical increase in safety against deteriorating flexibility and operability. If we don't signal the second train into the same platform somehow, then it'll probably just have to be held at a red signal and potentially cause delay to other trains as well as itself. This itself has a safety consequence; more trains being brought to red signals means more opportunity for a SPAD to occur.......
However historically it was regarded as perfectly acceptable, and in truth there have been very few accidents and incidents because of it. At some places there wouldn't be enough platforms to keep to the rule, one train in one platform. Sometimes, subject to risk assessment, it is possible to argue for the perpetuation of permissive moves at a particular site. Other places have got mid-platform signals- I think of Manchester Piccadilly through platforms on the line to Oxford Road and Birmingham New Street. Such places do tend to have very short overlaps, in the range 20m to 50m; even so rather better than the tail lamp of the previous train that has a zero overlap.
In some places (pretty sure The Netherlands is one) the platform staff wheel out on the platform a portable stop marker signal that if battery fed from the platform trolley on which it is mounted- this tells the incoming train driver exactly where to stop (and thus choose an appropriate overlap for the circumstances) and once it has served its purpose they wheel it away again.
I don't know the history of the BTM mid platform markers (i.e. whether they pre-date the current signalling that I believe dates from the late 1960s/ early 1970s); not sure they are actually unique, but cannot think of an equivalent elsewhere. Not in the Rule Book but I guess in some local operating instructions; very Western Region- cheap and simple and serves the purpose, so can't see it being adopted as a national standard.
As Peter said, there is less concern about terminal platforms particularly if the approach visibility is good. It is all about controlling risk and balancing any theoretical increase in safety against deteriorating flexibility and operability. If we don't signal the second train into the same platform somehow, then it'll probably just have to be held at a red signal and potentially cause delay to other trains as well as itself. This itself has a safety consequence; more trains being brought to red signals means more opportunity for a SPAD to occur.......
(19-08-2011, 12:39 PM)Peter Wrote:(19-08-2011, 08:13 AM)fil Wrote: Hi,
Am I right in thinking that permissive working is not an acceptable means of working for anything other than coupling trains?
If so, how do we control platform sharing? Signals mid platform seems the obvious solution but how would one get the required overlap?
Thanks
If you are looking at how permissive platform working has been used rather than what is stated as preferred today, have a look at places like the main London termini (Paddington, Waterloo etc) or at places where services start / terminate / divide en route (Eastleigh, Haywards Heath spring to mind). Bristol Temple Meads is an interesting case study on platform sharing because of the way the route indicator effectively gives the driver the authority (or not) to pass the mid platform "signal" which never changes its indication.
If you can find out about how it has been used, you will appreciate some of the risks that may be present and see why is may not be appropriate for general use, but if the relevant risks can be controlled, perhaps not ruled out totally.
PJW