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Author Topic: Allowances - what are they?  (Read 1707 times)
grahame
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« on: January 05, 2018, 09:06:45 am »

Here's the Real Time Trains schedule for this morning's 08:49 Swindon to Westbury



What do the allowance mean, and what should I read into them?
Eng?
Pth?
Prf?

I had previously understood that "Pth" was "Pathing" - in other words a train slowed down to keep it out of the way of something else later in it's journey.    And from that I concluded that a service showing significant "Pth" through Melksham but not stopping there would be operationally easy enough to call if we made a business case - especially if there was a precedent for that type of train calling at Melksham.   However, I'm told I'm wrong ... 13 minutes of Pth isn't enough to add a call.   Can someone explain, or might you suspect (like I do) that I'm being fed a porkie?



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bradshaw
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« Reply #1 on: January 05, 2018, 09:15:11 am »

The pathing in this case seems to allow a SWR Bristol -Salisbury train to pass Trowbridge before the Melksham service gets to the mainline. I does not appear on some of the other services.
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stuving
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« Reply #2 on: January 05, 2018, 09:44:45 am »

The information you need should be in the national section of the Timetable Planning Rules. And some of it is - though it's not really a technical manual of how to do timetabling, which is what you want.

It does list the timing elements and adjustment, including pathing/engineering/performance allowances inter (many) alia, but only says anything more about engineering recovery allowances.

Anyway, happy reading!
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grahame
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« Reply #3 on: January 05, 2018, 09:52:06 am »

The pathing in this case seems to allow a SWR Bristol -Salisbury train to pass Trowbridge before the Melksham service gets to the mainline. I does not appear on some of the other services.

I agree with you and that 08:49 is a slower service.  

But all is not what it seems. There are other services at times of engineering changes that also have what appears to be padding marked "pth" in them - up to 13 minutes in some cases and services that skip Melksham. However, I'm told that there isn't enough time within those specific schedules to make the stop. So it looks like I don't fully understand "pth" (or it's a convenient excuse to give ...).

The information you need should be in the national section of the Timetable Planning Rules. And some of it is - though it's not really a technical manual of how to do timetabling, which is what you want.

It does list the timing elements and adjustment, including pathing/engineering/performance allowances inter (many) alia, but only says anything more about engineering recovery allowances.

Anyway, happy reading!

Hmmm ... weekend reading, I fear.   Thank you.
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rogerw
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« Reply #4 on: January 05, 2018, 05:39:43 pm »

My understanding is that, as a rule of thumb, a station stop generally adds 5 minutes to a schedule. Bearing in mind that the speed limit through Melksham is only 40mph, 13 minutes pathing allowance should more than cover a stop.  This cold be crucial in March when the line through Newbury is closed and the daytime TransWilts service seems to completely disappear.  Having said that the diverted services appear to be running non-stop from Swindon to Westbury.
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grahame
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« Reply #5 on: January 06, 2018, 03:24:13 pm »

My understanding is that, as a rule of thumb, a station stop generally adds 5 minutes to a schedule. Bearing in mind that the speed limit through Melksham is only 40mph, 13 minutes pathing allowance should more than cover a stop.  This cold be crucial in March when the line through Newbury is closed and the daytime TransWilts service seems to completely disappear.  Having said that the diverted services appear to be running non-stop from Swindon to Westbury.

Discussion on that is ongoing ... apparently the 13 minutes does not cover the stop.

Issues tomorrow too - with Bath to Bristol closed, Portsmouth - Cardiff has become Portsmouth - Swindon.  Alternate trains in each direction have Melksham calls - EXCEPT that there's nothing northbound from 08:29 to 12:06.  No bus either.   Rather oddly, the 09:59 from Trowbridge passes through at about 10:08 and has 2.5 minutes of pathing allowance and takes 20 minutes between Trowbridge and Chippenham rather that the usual 18 or 19 for similar units with a stop at Melksham.   Scratching my head and asking "why not stop what would be the busiest train of the day", and not coming up with any logical answer.

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grahame
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« Reply #6 on: January 07, 2018, 07:59:22 pm »

Rather than go absurd early (08:29) or miss my own meeting (12:06), I caught that 09:43 the other way and changed at Trowbridge.

On time off Trowbridge
Slowed through Melksham at 10:07
Halted before Thingley Junction for that 2.5 minutes Pth (Bath - Swindon HSTs crossed ahead)
S-l-o-w run into Chippenham because we were behind the HST
On time into Chippenham

Still don't understand why there was a signal stop at the top of the single line rather than a Melksham stop in the schedule.

Evening - back in at 17:43.   14 off an 2 on.   Amazing considering that was a return working for what should have been the busiest Melksham departure of the day.  I wonder how much extra revenue GWR could have taken had they called on what would be the peak service on Sunday morning!
« Last Edit: January 07, 2018, 09:48:30 pm by grahame » Logged

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