ATP ATO Collective Questions 2013 to 1999

[asrisaku]

Hi Guys

This might give an idea how to start reading ATP and ATO focused on the IRSE MOD3 questions.

It looks like it is a common question that we can see from statistic.

PS: I need to work out these questions and I feel not confident when I try to answer them.

Best regards, Arnut

[PJW]

2013 Q4 is certainly closely related with ATO / ATP and potentially an ATP system could be one means of mitigating the consequences of an error made by the signaller when authorising a driver to pass a signal at danger and thus feature in Q3 and perhaps also feature as part of the answer to Q6.
I'd be surprised nowadays if it didn't feature at all- but as ever it is a matter of answering the actual questions asked, not just swotting up facts on certain technologies

Hi Guys

This might give an idea how to start reading ATP and ATO focused on the IRSE MOD3 questions.

It looks like it is a common question that we can see from statistic.

PS: I need to work out these questions and I feel not confident when I try to answer them.

Best regards, Arnut

[asrisaku]

Thanks PJW for making comments!

I was wondering ATP can be implied as Cab signalling?
Can TPWS be implied as ATP?
Is there any possibility to have SPADs when we have ATP system on? Human input error about train length, max permissible speed, track data, speed restriction?
When people say ATP is a failed safe system, what does it mean? Safe movement when anything is failed? Is it possible to have malfunction in ATP?
Is it true that ATP cannot have ability to detect train derailment?
Can TPWS and ATP work together? Is it called TPWS-E?

Thanks in advance if you can help me out.

Best regards, Arnut

[Peter]

Thanks PJW for making comments!

I was wondering ATP can be implied as Cab signalling?

Not necessarily. An ATP system may give you information in the cab about what is permitted, but it may not. ATP on the Great Western mainline gives you information about speed and limited information about signal aspect, but you could have an ATP system which is more of a background system and hence no possibility of "driving the train" without lineside signals because it does not give you any information.

Can TPWS be implied as ATP?

Not really. ATP systems generally provide continuous speed supervision and TPWS will not achieve that. Also, TPWS will not necessarily prevent a SPAD (merely mitigate the effects of one) and ATP systems are generally designed to stop the train before the signal.

Is there any possibility to have SPADs when we have ATP system on? Human input error about train length, max permissible speed, track data, speed restriction?

Speaking for GW-ATP, yes, the train data can be enters incorrectly and hence the margins of safety could be reduced to the point that a SPAD could occur, but with the relatively fixed formations, we are only talking about marginal issues (the braking of a 10 car unit is not going to be vastly different to an 8 car unit so the SPAD would be at low speed. Like all design and testing, it is f course possible to put the wrong trackside data in, but the independence of the two processes should reduce this risk.

When people say ATP is a failed safe system, what does it mean? Safe movement when anything is failed? Is it possible to have malfunction in ATP?

Of course, you can still have wrong side failures of equipment so certain failure modes will degrade safety. What is generally meant by fail safe in this context is that the system is self monitoring and slows the train when it detects an anomaly. Fr instance, each signal beacon tells the train the position and number of the next beacon so if the next one is not working or missing, the system knows this and alerts the driver accordingly. Similarly, if the oximetry is not working properly, the driver gets a warning if the next beacon is detected too early (under reading the actual distance travelled) or too late (over reading).

Is it true that ATP cannot have ability to detect train derailment?

Not sure what you are asking here.

Can TPWS and ATP work together? Is it called TPWS-E?

TPWS-E was a concept of implementing TPWS functionality using Eurobalise equipment. Since TPWS merely uses two frequencies to allow the train to measure its speed or to stop the train at an energised TSS, using the packet 44 information which varies according to the signal aspect and spacing the Balises in the same way as TPWS arm and trigger loops are spaced, the same result can be achieved. To my knowledge, there was only one trial in the UK with Siemens equipment fitted at five sites on the down main between Paddington and Reading with one FGW class 43 loco fitted with the receiving equipment. The trail ended over the years ago and was to pursued. Using this method, it would have been possible to implement TPWS functionality on an ETCS fitted train, so sort of giving what you asked of having an ATP system and TPWS working together.

Thanks in advance if you can help me out.

Best regards, Arnut

Peter

[PJW]

I think I need to correct an impression that may have been given by Peter's answer.

A full ATP system is likely to reduce the likelihood of a SPAD because it will be braking a train as it approaches a signal at red, BUT it will NOT stop the SPAD. There has to be a tolerance to compensate for the odometry uncertainty, so whereas the speed will be severely limited it has to allow the driver to drive right up to the signal and hence even past it. The ATP is designed to ensure that the "release speed" at which it permits the driver to SPAD is low enough that the ATP can be sure that it will stop the train by the defined safe place (generally the end of the overlap)- i.e. once it is certain that the train really must have passed the signal, it can then put on the emergency brakes and have enough distance left that it stop the train from the limited speed. Therefore ATP should reduce the consequence of the SPAD to zero (always remembering that the things that actually stop the train are the brakes and the adhesion between wheel and rail, either of which can fail but are typically not the responsibility of the signal engineer.)

The same is true in ETCS.

Indeed it is fundamentally the same in the CBTC metro world. However since often implemented without any lineside signals, then there is a view that no "overlaps" are provided- the truth is though that there is
1. a place where the Automatic Train Operation attempts to stop the train and
2. a separate place a little further on which is the place where the ATP guarantees to stop the train.
If you provide a large number of position references on the approach to the stopping position, the odometry uncertainty can be kept very low and this helps minimise the distance needed between these two locations, but there is always a minimum distance between where it "should stop" and where it "must stop". Such a safety margin may not always be very obviously there, but it does exist. You can call it an overlap beyond the stopping position or you can say that the train should stop a little prior to the full distance, but this is just playing with words.

[asrisaku]

Thanks Peter and PJW for kindness explanation.

Is it true that ATP cannot have ability to detect train derailment?
Not sure what you are asking here.

I was confused with the words from the attachment. It could be a different topic, I guess.

[PJW]

The extract was meaning that even if one had a 100% perfect ATP (itself a theoretical concept) then there will be some accidents since other things could go wrong. A train could derail owing to a rail defect or axle fracture.
The ATP cannot warn the driver if the rails have become wide to gauge, or all the stretcher bars on the points have become ineffective, the sea wall has become washed away leaving the rails suspended in mid air etc.
Accidents can still happen even if there is no driver error and no signalling malfunction; not everything is preventable by ATP. Therefore when assessing the safety benefit of providing ATP so that a proper consideration can be made re whether it justifies its cost, then have to recognise that some of the accidents would still occur.

Thanks Peter and PJW for kindness explanation.

Is it true that ATP cannot have ability to detect train derailment?
Not sure what you are asking here.

I was confused with the words from the attachment. It could be a different topic, I guess.