Hi Laura & Hitesh
Laura, long... time no see. I hope that the southern hemisphere is treating you well.
Last Wednesday I had a session with the London Study Group and we looked at 2005 Q6, which is uncannily similar to this one. Take a look at my answer to that which is here: http://irseexam.co.uk/showthread.php?tid=604 . Note that my answer is probably a little shorter than I'd want it to be for the exam. So I'll leave you to judge whether or not the length of yours were appropriate.
Some general thoughts having read what you wrote:
I noted that Laura's was presented in a table - a hazard log, this is a good idea.
You have stated no assumptions and for your answer to stack up I think it is important that you do.
I think that one of the key hazards is the relative crash worthiness of the stock, a freight train would crush a tram - is that a hazard or an escalated consequence? Depends on your system boundary, an assumption that a hazard is considered to be any precursor, escalating factor, or exposure of risk will allow you to include this and give the examiner confidence that you understand what you are writing about.
You could fairly assume that trams are as per Croydon/Nottingham with low platforms and a casual public approach to the 'secure off road sections', hence safety of the public who frequently tresspass.
Indeed passengers standing at platforms where every tram stops (my assumtion and it helps us to clarify another hazard so its worth making) being startled / struck by a freight at 100 km/h.
Ideally I'd run the freight in the night time out of tram operating times, and I'd state that. But the question says they have to run at the same time, so I'd note that it takes the freight 6 minutes to get through this shared section 10km long at 100km/h. The trams only run at one every ten minutes in the peak, so off peak you could run a freight train only when there are no trams in the shared section, (that may be too operationally restrictive) or more realistically split the shared section in half. This is more straight forward than asking a signaller to double block which exposes us to greater human error as your asking signaller to take decisions more often - higher workload and increased frequency.
I never thought of misrouting and its really relevant - imagine a freight being sent down the high street! Why no mitigation?
Can you guarantee axle counters will be activated by a 'flimsy' tram wheel?
Part iii which is only answered by Hitesh: A safety case is a good idea; but that is WHERE you demonstrate method of operation is acceptable - not HOW. You say " to demonstrate... that the risk associated with the operation has been managed and reduced to an acceptable level (ALARP)". I think this phrase is the one you should be concentrating on. You should write more about the ALARP principle which I discuss in the final part of the question I mention above (go to the Yellow Book for the real detail) - this is the perfect opportunity to draw an ALARP carrot and talk about tolerable risk, broadly acceptable risks etc. If you are sitting module 1 it would be exam suicide not to be able to produce half a page of A4 (diagram included) on this topic in less than 3 minutes.
Hope this helps???
In addition it has just occured to me that there are footpath crossings on Croydon's off road secure sections, that may be tolerable with trams (good braking) at 80km/h, but freight trains brake relatively poorly. Should we close the footpath crossings or reduce the line speed to 80kmh over the foot path crossings which don't give the crossing user necessary sighting time of an approaching freight train?
Laura, long... time no see. I hope that the southern hemisphere is treating you well.
Last Wednesday I had a session with the London Study Group and we looked at 2005 Q6, which is uncannily similar to this one. Take a look at my answer to that which is here: http://irseexam.co.uk/showthread.php?tid=604 . Note that my answer is probably a little shorter than I'd want it to be for the exam. So I'll leave you to judge whether or not the length of yours were appropriate.
Some general thoughts having read what you wrote:
I noted that Laura's was presented in a table - a hazard log, this is a good idea.
You have stated no assumptions and for your answer to stack up I think it is important that you do.
I think that one of the key hazards is the relative crash worthiness of the stock, a freight train would crush a tram - is that a hazard or an escalated consequence? Depends on your system boundary, an assumption that a hazard is considered to be any precursor, escalating factor, or exposure of risk will allow you to include this and give the examiner confidence that you understand what you are writing about.
You could fairly assume that trams are as per Croydon/Nottingham with low platforms and a casual public approach to the 'secure off road sections', hence safety of the public who frequently tresspass.
Indeed passengers standing at platforms where every tram stops (my assumtion and it helps us to clarify another hazard so its worth making) being startled / struck by a freight at 100 km/h.
Ideally I'd run the freight in the night time out of tram operating times, and I'd state that. But the question says they have to run at the same time, so I'd note that it takes the freight 6 minutes to get through this shared section 10km long at 100km/h. The trams only run at one every ten minutes in the peak, so off peak you could run a freight train only when there are no trams in the shared section, (that may be too operationally restrictive) or more realistically split the shared section in half. This is more straight forward than asking a signaller to double block which exposes us to greater human error as your asking signaller to take decisions more often - higher workload and increased frequency.
I never thought of misrouting and its really relevant - imagine a freight being sent down the high street! Why no mitigation?
Can you guarantee axle counters will be activated by a 'flimsy' tram wheel?
Part iii which is only answered by Hitesh: A safety case is a good idea; but that is WHERE you demonstrate method of operation is acceptable - not HOW. You say " to demonstrate... that the risk associated with the operation has been managed and reduced to an acceptable level (ALARP)". I think this phrase is the one you should be concentrating on. You should write more about the ALARP principle which I discuss in the final part of the question I mention above (go to the Yellow Book for the real detail) - this is the perfect opportunity to draw an ALARP carrot and talk about tolerable risk, broadly acceptable risks etc. If you are sitting module 1 it would be exam suicide not to be able to produce half a page of A4 (diagram included) on this topic in less than 3 minutes.
Hope this helps???
In addition it has just occured to me that there are footpath crossings on Croydon's off road secure sections, that may be tolerable with trams (good braking) at 80km/h, but freight trains brake relatively poorly. Should we close the footpath crossings or reduce the line speed to 80kmh over the foot path crossings which don't give the crossing user necessary sighting time of an approaching freight train?