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Author Topic: What is a "pathing allowance"  (Read 1653 times)
grahame
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« on: November 15, 2020, 04:56:33 pm »

Reading sometime on Real Time Trains ( https://www.realtimetrains.co.uk/train/U39055/2020-11-15/detailed ) I notice pathing allowances in the working timetable of 4 minutes at Bradford Junction and 6 minutes at Bath Spa - see attachment.

My understanding was that this means that there is 4 extra minutes in the timetable at Bradford Junction, and then 6 minutes at Bath, which isn't needed for the train to run between the points, but is there to avoid it arriving somewhere further down the line too early / at the same time as another train.

But I must be wrong ... the train in question is timetabled (in the working timetable) to take less than the four minutes between each of the timing points around Bradford Junction, and less than six minutes between each of the timing points around Bath Spa.   Can someone explain to me please?   Screen captures attached.
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stuving
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« Reply #1 on: November 15, 2020, 05:45:09 pm »

There are definitions in the national TPR (The Pensions Regulator) section of the Operational Rules. However, "pathing allowance" isn't defined. I understand it to be any of a number of allowances that depend on other trains. Times are based on sectional running times, which may depend on the train itself, plus its station calls. Engineering and recovery time allowances may be present. Those don't depend on other trains, so pathing is the rest - but I think it only gets applied where there is a signal, since a signal check is how the train would actually be delayed.

The two main types of pathing allowance are headway (if your train is faster than the one in front) and junction allowance (if another train on a conflicting path is within the safety margin). How RTT» (Real Time Trains - website) represents any of this is another matter. And, as you'll find in you look in the TPR, all of this is much more complicated and rests on some barely comprehensible distinctions.
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broadgage
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« Reply #2 on: November 15, 2020, 05:52:54 pm »

I would say,

"An extra time inserted in the working timetable, between the theoretical time required, and the actual time allowed for a journey. Primarily to allow for slight delays in awaiting a path. The timetable should be planned so as to avoid having to wait for a path, if however other services are running late then the train question may have to wait."

Example; An express train from the West country is due to pass west worzelshire junction at 10-40, five minutes after a local train. Last year the local service was often a few minutes late, and the express therefore held at signals before the junction. So this year a pathing allowance of 3 minutes has been added to the working timetable for the express.

An alternative policy might be to hold the late running local clear of the junction until the express had passed. In that case the pathing allowance would be applied to the local.

Despite planning, delays approaching a congested London terminus are likely, and a pathing allowance therefore added.

Excessive pathing allowances have become known as "charter minutes"
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A proper intercity train has a minimum of 8 coaches, gangwayed throughout, with first at one end, and a full sized buffet car between first and standard.
It has space for cycles, surfboards,luggage etc.
A 5 car DMU (Diesel Multiple Unit) is not a proper inter-city train. The 5+5 and 9 car DMUs are almost as bad.
stuving
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« Reply #3 on: November 15, 2020, 06:49:57 pm »

What I called "junction allowance" is actually called junction margin. This is what the national TPR (The Pensions Regulator) has to say on the topic, as an example of what goes on:
Quote
6.6 Junction Margins
6.6.1 The values listed in Section 5.3 of the TPR are Junction Margins and Station Planning Rules. 6.6.2 A Junction Margin is the minimum permissible time interval between two trains that are performing conflicting moves at a timing point, such that the second train can meet its SRT. This is expressed in multiples of half minutes derived from the technical value expressed in seconds.
6.6.3 Where necessary and appropriate, differential junction margins shall be created for different combinations of:
  • Train type (including weight, length and speed)
  • Stopping or passing movements
  • Diverging or converging movements
For example, a train accelerating from rest across a junction will require a greater margin to avoid impact on the second train, than a train crossing the same junction at line speed. The stopping pattern of both trains must also be taken into account so that acceleration or deceleration relative to line speed is taken into account.
6.6.4 The calculation of a junction margin consists of a number of components:
1) Time taken between the front of the first train passing the timing point and its rear clearing the relevant track circuit or axle counter 
2) Time taken for the signaller or ARS (Automatic Route Setting) to reset the route and the signals to clear for the second train
3) Time taken between the second train sighting the relevant signal, such that it can meet its SRTs, and its front passing the timing point
6.6.5 A basic junction margin is the sum of 1, 2 and 3 rounded to the next half-minute above to form the planning margin.
6.6.6 If this does not provide a sufficient performance buffer, performance uplift will be added. This will be an agreed uplift to the sum of the 1 and 3, before adding 2 (this is fixed) and finally rounding to the next half-minute above or below. For example, train 1 takes 73 seconds to clear the relevant track circuit after leaving the timing point (1). The signaller takes 9 seconds to reset the route for train 2 across the junction (2). In order for train 2 to meet its SRTs, the train takes 62 seconds to reach the timing point for the junction (3). Ergo, the margin is (73 + 9 + 62) seconds = 144 seconds, + 6 seconds uplift to round up to 150 seconds, with any additional uplift agreed as appropriate. 6.6.7 Network Rail will seek to model most combinations of stopping and non-stopping trains for passenger and freight services as agreed with stakeholders.

There is also a diagram, which may make that explanation clearer ... if only slightly.
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PhilWakely
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« Reply #4 on: November 15, 2020, 09:29:41 pm »

'Pathing Allowance' has always puzzled me with respect to Network Rail's Flying Banana trip down the Mule. It is timed to take 10 minutes between Pinhoe and Exmouth Junction, a distance of just over 1 mile and this is down to '1 minute engineering allowance, 8 minutes pathing allowance'.

Looking at trains due through Exmouth Junction, there is an Exmouth train crossing the junction 3 minutes before the Banana is scheduled to pass, so maybe this has something to do with it. Invariably, the Banana does go through the Junction well before the Exmouth train.

Also, when passing back through Pinhoe, the Banana has a 7 minute pathing allowance between Exmouth Junction and Pinhoe. Invariably the Banana will be waiting at Pinhoe for those 7 minutes whilst it waits for the preceding Waterloo train to reach Feniton.

https://www.realtimetrains.co.uk/train/H17600/2020-11-19/detailed

So, I can understand the pathing allowance on the second pass of Pinhoe as NR» (Network Rail - home page) wouldn't want to advertise the stop at Pinhoe, but I would have thought the earlier pass would have been described as Junction allowance.
 
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IndustryInsider
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« Reply #5 on: November 15, 2020, 09:45:10 pm »

I think you?re all misunderstanding the reason Graham is asking the question.  Wink
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stuving
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« Reply #6 on: November 15, 2020, 11:34:14 pm »

I think you?re all misunderstanding the reason Graham is asking the question.  Wink

Or just not answering the second question - why do RTT» (Real Time Trains - website)'s timings not reflect that allowance at the point it's meant to apply to - for want of knowing the answer. But I have a couple of pointers, which someone may know more about.

Firstly, I think RTT shows times for places that are not timing points in the WTT (Working Time-Table). For stations where a train calls, it will have times in the WTT, but they may not be timing points for trains that don't call. For example, if you look at OTT (Open Train Times website) or Liverail for that engineering train (6G70) there's no times shown between Bath Spa and North Somerset Junction. Secondly, if you look at another goods service on that route today - such as 013K due out of Westbury for Stoke Gifford at 1304 - it has smaller allowances and shorter times between those true timing points. True it's timed for 75 mph not 60, but the differences are bigger than that.
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stuving
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« Reply #7 on: November 15, 2020, 11:58:37 pm »

Confirming what I said about timing points, the Western Route TPR (The Pensions Regulator) has this note above its list of timing points:
Quote
In the tables below, the following codes apply:
F Only freight trains are timed here
P Only passenger trains are timed here
S Only stopping trains are timed here
X Only trains crossing from one running line to another are timed here

So those are the main types of optional timing point (others are shown with individual notes). The bit of the list for GW105 from Bath has this:
TIMING POINTCODE    NOTES
Bath SpaPlatform detail must be shown.
Bath Goods Signal B175XFor use when train is using Down main
from Bristol direction.
Bath Goods LoopS
Bath RTSS
Oldfield ParkSPlatform detail must be shown.
KeynshamSPlatform detail must be shown.
Bristol East DepotS
Bristol East Depot DGLS
North Somerset Junctiondetail omitted
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grahame
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« Reply #8 on: November 16, 2020, 06:21:07 am »

I think you?re all misunderstanding the reason Graham is asking the question.  Wink

Or just not answering the second question ....

Thanks for that, IndustryInsider and Stuving for following up ... I thought I was missing something as I read all the original answers which provided a fascinating read - a formalisation of process that I knew must exist, but knew lilt about, but skirted round my question to the extent of not answering it.

I conclude ... a "Pathing allowance" is added at a timing point (for travel from there to the next timing point), but there are sometimes quite long distances between timing points and that extra time may be "spread out" along the way.  Real Time Trains (in its working timetable column) calculates extra, unofficial, times between timing points to give a time when the train might be best expected to pass that location and as such the extra minutes get spread out along the way and may not be seen in the times immediately adjacent to where the minutes are flagged up.

The example I picked up - six minutes at Bath Spa - went through Bath Spa 21 minutes early, and then gained 5 minutes before the next official timing point on the outskirts of Bristol, which illustrates this spread (and that the train in question was so early it 'made' a new path at a quieter time on the line)

Thank you all for the answers!
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« Reply #9 on: November 16, 2020, 12:42:15 pm »

Despite planning, delays approaching a congested London terminus are likely, and a pathing allowance therefore added.

Excessive pathing allowances have become known as "charter minutes"

I think that's two separate things.  What has become known as "charter minutes" is just extra time added to the public timetabled arrival against the WTT (Working Time-Table) arrival.  It happens on many services, and this time of year is even more prevalent due to leaf fall. 

Then you have some trains which have a "performance" allowance which are (along with an "engineering" allowance, as well as the "pathing" allowance already discussed) the three different ways the WTT schedules can have allowances for different things added.  But this is different to what you could call a "performance allowance" in terms of massaging the figures.  The schedule below (Chiltern always exploit it to the maximum) shows engineering and performance allowances, but no pathing allowances, yet is has still got a GBTT (Great British Time Table) arrival time 5 minutes after the WTT time.  The GBTT time is what the charter performance figures are calculated on. 
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« Reply #10 on: November 16, 2020, 05:54:58 pm »

'Pathing Allowance' has always puzzled me with respect to Network Rail's Flying Banana trip down the Mule. It is timed to take 10 minutes between Pinhoe and Exmouth Junction, a distance of just over 1 mile and this is down to '1 minute engineering allowance, 8 minutes pathing allowance'.

Looking at trains due through Exmouth Junction, there is an Exmouth train crossing the junction 3 minutes before the Banana is scheduled to pass, so maybe this has something to do with it. Invariably, the Banana does go through the Junction well before the Exmouth train.

Also, when passing back through Pinhoe, the Banana has a 7 minute pathing allowance between Exmouth Junction and Pinhoe. Invariably the Banana will be waiting at Pinhoe for those 7 minutes whilst it waits for the preceding Waterloo train to reach Feniton.

https://www.realtimetrains.co.uk/train/H17600/2020-11-19/detailed

So, I can understand the pathing allowance on the second pass of Pinhoe as NR» (Network Rail - home page) wouldn't want to advertise the stop at Pinhoe, but I would have thought the earlier pass would have been described as Junction allowance.

As far as I can see, junction margin is shown as part of pathing allowance, so you won't see a separate figure. There's a lot about measurement trains (and other NR paths) in the national section of the TPR (The Pensions Regulator), since they need to be timetabled but don't run every day. So there is a draft timetable for two years ahead, and they try to fit them in so no-one gets upset, but evidently don't always succeed. The format of this has changed recently, so the process may also have changed - but like all things railway, don't expect anything rapid.

While de-icers and RHTT (Rail Head Treatment Train) run daily when needed, measurement trains are mostly on a four-week or eight-week cycle. (Incidentally, there is another listed two-way run on the Mule every eight weeks, but I can't see it at the moment in the WTT (Working Time-Table).) That gives NR a bit more leeway to delay other trains - after all, TOCs (Train Operating Company) accept that stuff happens at that sort of frequency. A few are even less frequent, and are just shoehorned in as STP as and when. I guess the measurement trains work best at line speed, so they don't like then to keep ducking out of the way, though on a single line that may not be possible.
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