You are correct- It would be very surprising if NR were to comision any new AOCL; further I would anticipate existing ones would probably be converted when major renewal needed.
An ABCL should be providing a white flashing light for the rail driver prior to the time that the train arrives at the commencement of the crossing speed restriction- these boards are positionrd such that there is braking distance from the signed speed to a stop before reaching the roadway. So you first need to decide what that speed is to be (depends on crossing inter-visibility). Then you need to position the strike-in so that a train approaching at line speed and then braking to comply with the crossing speed will give the crossing enough time to operate- that means the 3 secs of yellow, then the 8secs of flashing red until the time that the barriers will be called down, because it is at that time that the DCI would start flashing white. Therefore it is a series of calculations- the important thing is to realise that we are seeking here to ensure that the train is not delayed waiting for the crossing; very different than for AHBC where the traiin will be going over that road at the maximum linespeed no mater what, so the crossing simply must close the road sufficientlly prior that the road user isn't there!
An ABCL should be providing a white flashing light for the rail driver prior to the time that the train arrives at the commencement of the crossing speed restriction- these boards are positionrd such that there is braking distance from the signed speed to a stop before reaching the roadway. So you first need to decide what that speed is to be (depends on crossing inter-visibility). Then you need to position the strike-in so that a train approaching at line speed and then braking to comply with the crossing speed will give the crossing enough time to operate- that means the 3 secs of yellow, then the 8secs of flashing red until the time that the barriers will be called down, because it is at that time that the DCI would start flashing white. Therefore it is a series of calculations- the important thing is to realise that we are seeking here to ensure that the train is not delayed waiting for the crossing; very different than for AHBC where the traiin will be going over that road at the maximum linespeed no mater what, so the crossing simply must close the road sufficientlly prior that the road user isn't there!
(26-08-2012, 09:51 AM)alexgoei Wrote: Hello PJW,
Hope you are fine. Its the time of year when those taking the Module 2 exams need the revision and practice hence the visit to the forum.
Appended please find the summary comparing ABCL, AOCL, AHBC and MCB which I had submitted to you in late May this year for your comments. Thank you for your valued comments and for the benefit of others taking the module 2 exams I would like to post them here complete with your comments on my summary.
Level crossings are included in almost every other year if not every year.
From the ORR Guide that I reviewed, AOCL is not favoured by Network Rail for new crossings and so for the exams if we are signalling to UK mainline practice, AOCL need not be considered as an option. Please correct me if I am wrong to come to this conclusion.
My one question on your comments on the ABCL is that how will the SIP be determined without the 27 sec rule which you deleted?
Hope this summary is useful to all.
Cheers
Alex
PJW