RAIB has just published
an accident report where a wheelchair that had become stuck was hit by a train, the occupant fortunately having extracted themselves in the nick of time.
Quite a lot of useful information from a mod 1 and mod 5 perspective
Hi,
I have a query related to AHBC controls.
There is a protecting Signal near to AHBC and it is less than 800m from the crossing. There is a regulation on that signal clearance. Do we include any AHBC Normal conditon in the Signal Control Table other than the note related to Signal regulation.
As there will be AHBC control Table separately, I dont think that the AHBC normal condition is required in the Signal Control Table.
Please correct me if am wrong.
Thanks & Regards
As you say, a signal really does not "protect" an AHBC level crossing; the crossing fundamentally protects the road by closing it a sufficient time before a train can arrive.
The signal, when ARAFOAL, prevents the AHBC from seeing the approaching train and in that circumstance has to take over the duty of protection. It does this by imposing a delay between when the AHBC can "see" a train and when the driver is authorised to proceed, thus ensuring that a full warning period is always given. The time is calculated on the basis of
1. determining how the fastest accelerating train (typically a powerful locomotive running "light engine" without a train to pull) could reach the crossing if it had been decelerating to a stop at the red signal which at the last minute then changes to green (generally the worst case is around 100m on the approach if I recall correctly),
2. comparing this to the total warning which the crossing needs (the minimum standard road user warning, addition for skew crossing, addition for equipment operation time etc, addition for Minimum Road Open Time if applicable),
3. if 2 >1 then the delay timer is the difference between time 2 and time 1.
Hence you are correct:
a) on the AHBC Control Table there will be a reference to the signal inhibiting strike-in,
b) on the signal Control Table there will be a reference only to the delayed clearance.
(20-11-2012, 06:13 AM)jenni.joseph9 Wrote: [ -> ]Hi,
I have a query related to AHBC controls.
There is a protecting Signal near to AHBC and it is less than 800m from the crossing. There is a regulation on that signal clearance. Do we include any AHBC Normal conditon in the Signal Control Table other than the note related to Signal regulation.
As there will be AHBC control Table separately, I dont think that the AHBC normal condition is required in the Signal Control Table.
Please correct me if am wrong.
Thanks & Regards
Hi,
Thanks alot for the reply.
I have a similar query related to MCB. I am attaching the layout for clear picture of the scenario which I am studying.
Signals S5 and S4 have predominant moves in the Down and up directions respectively where as S7 and S6 have only the Turn back moves. There is a crossing with name XXXX MCB(OD) LC.
Signals S7 and S6 have a note on them saying that XXXX MCB(OD) LC is initiated when S7 or S6 called to clear.
Now, for signals S5 and S4 the XXXX crossing normal proving is required in the Aspect level of signal control table. But do we ensure the same for Siganls S7 and S6?
As the train always start from rest for Signals S7 and S6, how the initiation of the barriers is ensured? The actual Initiation of the barriers start only when the signal S7 and S6 are called to clear, right?
So, in the Signal control table of S7 and S6, there should be a note in the Aspect level, that the Initiation of the barriers happens only when the signals are called to clear. Please correct me, if am wrong.
Thanks & Regards
Do I assume correctly that the (D) stands for "Obstacle Detector"? In which case this is not something I have dealt with or even read upon being a new development and not a concern to me at work currently.
I think that in time the idea is to replace the need for the signaller to observe the crossing and give a Crossing Clear by undertaking a radar sweep of the crossing when booms down to ensure that there is nothing (over a certain size) trapped. As I understand it, initially it is introduced just as reinforcement of the signaller observation. However in this regard I don't see a large difference from a normal MCB / CCTV crossing.
For the normal running, one assumes that the crossing is commenced to auto lower by the arrival of teH incoming train within the relevant strike-in zone at a time when all routes are set from it up to and beyond the road. Should a route not be set, then there would be no strike-in but as soon as the route is set then the crossing would be initiated, the signal obviously remaining red until the barriers down and the crossing proved clear (by whatever means).
I don't see that S6 & S7 would be different, other than the fact that by their nature the train will always be there first and hence the setting of the route will always be the trigger for the crossing sequence to commence. I do not perceive there would be any further delay other than that taken for the crossing to respond and be proved clear as above.
I would certainly expect exactly the same proving of the crossing in the aspect of all signals reading over the roadway- you stated "normal" but that is a poor phrase to use given that the crossing is normal (at least in the UK) when the barriers are raised. So that is the "Crossing Clear" non-replacing and the various controls summated in the "barriers locked down" function in the aspect dead.
So I agree with you- from a Control Table presentation I think i'd expect all to be the same: crossing initiated by routes set when relevant tracks are not clear; it is just that it could be that for some reason it has been decided to simplify the circuitry in the case of 6 & 7 and use the "nearly aspect" relay to start the crossing and perhaps that is hy the CT presentation differs.
(08-12-2012, 01:08 PM)jenni.joseph9 Wrote: [ -> ]Hi,
Thanks alot for the reply.
I have a similar query related to MCB. I am attaching the layout for clear picture of the scenario which I am studying.
Signals S5 and S4 have predominant moves in the Down and up directions respectively where as S7 and S6 have only the Turn back moves. There is a crossing with name XXXX MCB(OD) LC.
Signals S7 and S6 have a note on them saying that XXXX MCB(OD) LC is initiated when S7 or S6 called to clear.
Now, for signals S5 and S4 the XXXX crossing normal proving is required in the Aspect level of signal control table. But do we ensure the same for Signals S7 and S6?
As the train always start from rest for Signals S7 and S6, how the initiation of the barriers is ensured? The actual Initiation of the barriers start only when the signal S7 and S6 are called to clear, right?
So, in the Signal control table of S7 and S6, there should be a note in the Aspect level, that the Initiation of the barriers happens only when the signals are called to clear. Please correct me, if am wrong.
Thanks & Regards