Novice question - what is pathing time?

[HUY2ROB]

There been a few comments on a local Facebook group from people who missed seeing the Tornado on the return trip from York to Liverpool last night. By the time it reached Huyton it was twenty minutes ahead of schedule. I didn’t bother because I thought it would be too dark at 21-40, the due time. I checked on Real Time Trains and noticed it was going to be early. I had another look today and noticed that it had been on time at Manchester Victoria but made up twenty minutes before it got here. I also noticed that there was a total of eighteen minutes of pathing time at nine stations between Manchester and Huyton. It then lost eleven minutes in the two miles to Broad Green. How does pathing time work?

 

[jfollows]

Pathing time is extra time added to a train's schedule to recognise conflicts with other trains.
These conflicts will typically be seen when a faster train catches up with a stopping train, or two trains have conflicting movements across junctions which requires one of the trains to wait.
Timetables for regularly scheduled trains are constructed to minimise the need to use pathing time as much as possible.
Additional trains added to the schedule such as the one you're referring to (https://www.realtimetrains.co.uk/service/gb-nr:U13591/2021-09-16/detailed) have to fit in alongside other trains, and often this requires the additional trains to be held up because of them. There were lots of minutes of extra time in this schedule you mention because of other conflicting trains.

Essentially in our busy railway system it's not generally possible to schedule extra trains like the one you're referring to with totally clear paths, and this manifests itself in the form of pathing time added to the schedule.

EDIT The train you're referring to was 20 minutes early at Huyton, but was then held between there and Roby (where there's a four-track section specifically designed to allow trains to overtake) to allow 2C30 20:52 Wigan-Liverpool (https://www.realtimetrains.co.uk/service/gb-nr:L07225/2021-09-16/detailed#allox_id=0) to overtake it. 2C30 was running on time and your special train was still 9 minutes early at Broad Green, so it didn't "lose" 11 minutes unless you count deliberate regulation as loss!

Also, the primary reason the train was early at Huyton is because the St. Helens Junction stop 21:15-21:30 was omitted, so 3 minutes early became 18 minutes early instantly because of the omitted stop. Until then most of the pathing allowance seems to have been required.

(I'm guesssing now, but the St. Helens Junction stop wasn't a passenger stop, so it must have been "operationally more convenient" to omit it last night, but all that meant is that the special sevice got slowed down to let 2C30 go in front a few miles further on.)

 

[The Planner]

The biggest issue of using significant amounts of pathing time is that the running times will always assume you are moving, which when in use for a junction conflict you often won't be, especially if its more than a couple of minutes. This can often start producing delays as the train is actually at a stand when the running times assume you are at line speed. Its not often that a schedule will have time added to mitigate that.

 

[jfollows]

The biggest issue of using significant amounts of pathing time is that the running times will always assume you are moving, which when in use for a junction conflict you often won't be, especially if its more than a couple of minutes. This can often start producing delays as the train is actually at a stand when the running times assume you are at line speed. Its not often that a schedule will have time added to mitigate that.

That's an interesting and good point - I hadn't thought about this before but I can see exactly what you mean. It could mean that the new "Lumo" schedules between King's Cross and Edinburgh aren't good because they've got lots of pathing time included, which may not accurately reflect the length of time they'll end up being delayed by other services in reality as you say.

 

[_toommm_]

In the case of the train from York to Lime Street, it was booked to follow closely 2F11, the 19:17 Crewe to Lime Street stopping service. Even though most of the stops only have half a minute allocated to it in the Working Timetable (WTT), of course you lose time accelerating and decelerating, so pathing time (extra time essentially) was added every so often to account for this. As jfollows said, the stop at St Helens Junction was omitted so the charter ended up rather early. As the traffic becomes more intense as more lines join as it gets closer to Lime Street, that fifteen minutes that was planned at St Helens instead took place after Huyton.

 

[6Gman]

I shall bore you all with an anecdote which illustrates where pathing allowances can go very wrong.

A colleague of mine was responsible for timing a South Wales - Edinburgh rugby special. He made the mistake of accepting a handover time from the Western Region (at Craven Arms) and a handover time to the Scottish Region (at Gretna). Unfortunately the more he looked at it the more he realised that they were too far apart, so to speak. He timed it back from Gretna and it would be leaving Crewe around 1200. Unfortunately he'd already agreed a Craven Arms time of 0945. For a journey of around 50 minutes. So he came up with something like:

Craven Arms pass 0945
(20 minutes pathing allowance)
Shrewsbury pass 1030
(20 minutes pathing allowance to Whitchurch and 10 minutes further to Crewe)
Crewe arrive 1140 (for loco change)

On the day it got a clear road and arrived at Crewe at 1100 and sat, and sat, and sat. It turned a bit nasty as several hundred rugby fans wondered why they were sat (not on a platform road) for an hour as they cast envious glances at the station buffet.

 

[The Planner]

In the case of the train from York to Lime Street, it was booked to follow closely 2F11, the 19:17 Crewe to Lime Street stopping service. Even though most of the stops only have half a minute allocated to it in the Working Timetable (WTT), of course you lose time accelerating and decelerating, so pathing time (extra time essentially) was added every so often to account for this. As jfollows said, the stop at St Helens Junction was omitted so the charter ended up rather early. As the traffic becomes more intense as more lines join as it gets closer to Lime Street, that fifteen minutes that was planned at St Helens instead took place after Huyton.

Pathing time is to keep the charter at the planning headway at the mandatory timing points, its not technically for acceleration amd braking though that clearly occurs.

I shall bore you all with an anecdote which illustrates where pathing allowances can go very wrong.

A colleague of mine was responsible for timing a South Wales - Edinburgh rugby special. He made the mistake of accepting a handover time from the Western Region (at Craven Arms) and a handover time to the Scottish Region (at Gretna). Unfortunately the more he looked at it the more he realised that they were too far apart, so to speak. He timed it back from Gretna and it would be leaving Crewe around 1200. Unfortunately he'd already agreed a Craven Arms time of 0945. For a journey of around 50 minutes. So he came up with something like:

Craven Arms pass 0945
(20 minutes pathing allowance)
Shrewsbury pass 1030
(20 minutes pathing allowance to Whitchurch and 10 minutes further to Crewe)
Crewe arrive 1140 (for loco change)

On the day it got a clear road and arrived at Crewe at 1100 and sat, and sat, and sat. It turned a bit nasty as several hundred rugby fans wondered why they were sat (not on a platform road) for an hour as they cast envious glances at the station buffet.

They had a bit of a shocker there, should of held it back at Shrewsbury if they could.

 

[mmh]

Presumably "pathing time" is why for many years a "fast" service from Crewe to London I used many times would inevitably stop for 10-15 minutes at Rugby to allow a more important service to pass. I believe it was scheduled to do this.

Less understanding people might quite understandably have thought it was completely ridiculous.

 

[kentuckytony]

If this is inappropriate to the topic of pathing, the monitors can remove.

A somewhat related historical story about pathing,
This is a report about a train accident in 1906 that would not have happened if a superintendent changed the set paths and times of two trains.

It is from my local city's (Edgewood KY) history written by one of our councilmen Ben Barlage.

1906: Local Edgewood Farmer George Riley of Charter Oak was returning from Cincinnati on Tuesday February 13th. George boarded the Louisville & Nashville rail line. He boarded the Local 3:40 PM train, a light speedy Engine #100 piloted by Engineer Jim Mahoney pulling passenger cars from town and stopping at all stations along the way. The L&N operated both a local train service as well as a series of express trains that would run direct to major cities with no stops. Every day the local southbound train would pull off to the side at the Latonia Station to let the Express breeze by as it headed north to Cincinnati on the single track. As George’s train entered Latonia the station Superintendent Mr. Arnold informed Engineer Mahoney that the Express train, a heavy Engine # 228 was running about 17 minutes behind schedule. Plenty of time for the local train to cover the 3 miles to Maurice Station (Pioneer Park) and pull off to the side for the express. Since its completion in 1854 the L&N Railroad was making these north-south runs like clockwork. Taking pride in their timeliness, George’s train picked up the pace as Fireman Stout shoveled more coal on the fire. The Southbound train would surely make Maurice Station in record time. The train sped over the Banklick Creek bridge (across from present day Thorntons on 3L) at speeds exceeding 50 mph and began to make the tight blind curve south (around the Winding Trails hillside) as the Engineer leaned out from his engine to see the express bearing down upon him, scarcely 300 feet distant. He screamed a warning to his fireman and leaped from the engine. Fireman Moore of the express saw the impending danger and he too leaped. “An instant later the great roar and hiss of escaping steam, the crash as the two great hulks of steel met. And then the rending of wood and iron as it was torn apart like tissue. Both engines reared high in the air, reeled on their rear trucks and fell backward on opposite sides of the track.” The sound of the impact could be heard for miles around. (Impact occurring where present day 3L crosses over the L&N rails.) Two were killed, Fireman Stout of Engine 100 and Engineer Murphy of Engine 228 who did not have the opportunity to leap from the train. “Both trains were laden with passengers and the force of the collision threw them about in the coaches behind like so many wind-tossed straws. Many were painfully injured, but through some rare good fortune all the coaches remained on the tracks and injuries to passengers were confined to cuts and bruises.” A second rail car was dispatched to take injured passengers to St. Elizabeth Hospital in Covington. March 08, 1906 “Farmer seeks $50,000 damages” George Riley, Victim of Wreck at Maurice Station, Enters Action Against Railroad. George received injuries about his back and spine which were permanent.

 

[The Planner]

Presumably "pathing time" is why for many years a "fast" service from Crewe to London I used many times would inevitably stop for 10-15 minutes at Rugby to allow a more important service to pass. I believe it was scheduled to do this.

Less understanding people might quite understandably have thought it was completely ridiculous.

No, that is being overtaken with a long dwell. Pathing time keeps you behind a train. In that instance if your train was allowed to carry on, the following would have had pathing time added to keep it at the headway further down towards London. However, as it was clearly journey time dependent, your train gets looped.

 

[jfollows]

Presumably "pathing time" is why for many years a "fast" service from Crewe to London I used many times would inevitably stop for 10-15 minutes at Rugby to allow a more important service to pass. I believe it was scheduled to do this.

Less understanding people might quite understandably have thought it was completely ridiculous.

Also, if you can say when this service ran, I might have a working timetable which includes it which might shed more explanation on what was going on.

 

[6Gman]

They had a bit of a shocker there, should of held it back at Shrewsbury if they could.

They could have held it at Shrewsbury, but that would just have moved the issue to a less suitable location. (My recollection is that BTP got involved to emphasise that "no, you can't jump off the train to cross the tracks to the station buffet"; not sure Shrewsbury would have had a BTP presence at the time.)

The error was in accepting two handover times; it should either have been timed back from Edinburgh or forward from South Wales.

But we may be drifting a little too far from the thread topic.

(Though it does emphasise that pathing allowances are for a minute or three to maintain headways, not tens of minutes to cover errors! )

 

[The Planner]

They could have held it at Shrewsbury, but that would just have moved the issue to a less suitable location. (My recollection is that BTP got involved to emphasise that "no, you can't jump off the train to cross the tracks to the station buffet"; not sure Shrewsbury would have had a BTP presence at the time.)

The error was in accepting two handover times; it should either have been timed back from Edinburgh or forward from South Wales.

But we may be drifting a little too far from the thread topic.

(Though it does emphasise that pathing allowances are for a minute or three to maintain headways, not tens of minutes to cover errors! )

Standard Western, never accept back timing

 

[Watershed]

Trains are conventionally timed using "the graph", which essentially means a sort of distance-time graph plotting the geography of a line or route, against the hours and minutes. See below for an example:



On a completely blank graph with no trains, you wouldn't need pathing at all. The train you're timing would simply take as long as it takes to get from A to B. That in turn depends on the type and maximum speed of the train, as well as whether it calls at any intermediate locations.

But as soon as you have multiple trains competing to run along the same bits of track (or conflicting at junctions/stations), it will quickly become the case that one or more of the trains can't run as it optimally should - because there will be another train on the line in the way, or a conflicting move at a junction.

In other words, the line representing the train on the distance-time graph would cross another line (train), representing a conflict. That is not allowed unless it is a non-conflicting move (e.g. a fast train passing a freight train that's in a loop).

In all other cases, you need to allow the headway or junction margin between all trains - the default value is 3 minutes, but it varies widely depending on the signalling and track layout.

Pathing is the solution to this conflict. It is the purest form of "padding" in a sense, but it simply means that you add extra time to a train's schedule to keep it behind another train on the line ahead, or conflicting move at a junction/station.

Because with pathing you are artificially extending a train's schedule, if the train is running late, then it should (theoretically) be able to catch that time up. Similarly if, for example, a "runs as required" freight train, that it was pathed to run behind, is not running that day.

 

[30907]

That graph takes me back a decade or three, thanks!

 

[Spartacus]

In the case of the train from York to Lime Street, it was booked to follow closely 2F11, the 19:17 Crewe to Lime Street stopping service. Even though most of the stops only have half a minute allocated to it in the Working Timetable (WTT), of course you lose time accelerating and decelerating, so pathing time (extra time essentially) was added every so often to account for this. As jfollows said, the stop at St Helens Junction was omitted so the charter ended up rather early. As the traffic becomes more intense as more lines join as it gets closer to Lime Street, that fifteen minutes that was planned at St Helens instead took place after Huyton.

I had to read that a few times before realising you weren’t saying the pathing was inserted in the 2F11 to account for it’s stopping and starting!

 

[306024]

The biggest issue of using significant amounts of pathing time is that the running times will always assume you are moving, which when in use for a junction conflict you often won't be, especially if its more than a couple of minutes. This can often start producing delays as the train is actually at a stand when the running times assume you are at line speed. Its not often that a schedule will have time added to mitigate that.

Really? It was consistently applied when I worked with timers at a TOC who understood that basic requirement. Smacks of poor training if it isn’t being applied now.

 

[The Planner]

Really? It was consistently applied when I worked with timers at a TOC who understood that basic requirement. Smacks of poor training if it isn’t being applied now.

Never known it be taught at all.

 

[306024]

Never known it be taught at all.

You surprise me, but then again perhaps not. It's rather fundamental to good planning.

 

[Watershed]

Really? It was consistently applied when I worked with timers at a TOC who understood that basic requirement. Smacks of poor training if it isn’t being applied now.

It's a regionalised issue. Some regions don't mention it at all, others (e.g. the Western) have a table in the TPR where you can look up the appropriate adjustment allowance to use.

A lot of timetables simply couldn't be made compliant if you applied these allowances nationwide...

 

[Ianno87]

It's a regionalised issue. Some regions don't mention it at all, others (e.g. the Western) have a table in the TPR where you can look up the appropriate adjustment allowance to use.

A lot of timetables simply couldn't be made compliant if you applied these allowances nationwide...

There aren't many places I can think of in the rules where a running time must be adjusted if pathing time is applied in a previous section.

More common is application of a stop (and thus Stop/Start SRTs) in instances where the train would be brought to a stand, and pathing time would not properly allow for the train catching up back to normal speed again.

 

[The Planner]

There aren't many places I can think of in the rules where a running time must be adjusted if pathing time is applied in a previous section.

More common is application of a stop (and thus Stop/Start SRTs) in instances where the train would be brought to a stand, and pathing time would not properly allow for the train catching up back to normal speed again.

That has upset the performance guys in the past though if you add a stop at a junction instead of a chunk of pathing time as I think their was some idiosyncrasy where it picked up the arrival time as the departure and flagged a false delay.

 

[Tomnick]

Something that I've noticed seems to have crept in recently, in the context of diverted long(er)-distance passenger trains, is the insertion of stops (sometimes unadvertised, sometimes shown as public stops) at implausible intermediate stations on the diversionary route rather than using pathing time approaching a conflict. Any views from the experts?

Realtime Trains - 1R50 0437 Nottingham to Liverpool Lime Street

 

[306024]

Using stops at junctions rather than pathing time became more common in some areas as Automatic Route Setting expanded. It helped keep trains in the right order rather than have the timetable processor do something you didn’t want to happen.

There are so many different combinations of trains and infrastructure that writing rules for every interaction or conflict is a considerable task, and having written them would take a lot of understanding to apply correctly.

 

[The Planner]

Something that I've noticed seems to have crept in recently, in the context of diverted long(er)-distance passenger trains, is the insertion of stops (sometimes unadvertised, sometimes shown as public stops) at implausible intermediate stations on the diversionary route rather than using pathing time approaching a conflict. Any views from the experts?

Realtime Trains - 1R50 0437 Nottingham to Liverpool Lime Street

That looks genuine, as you have got other chunks of allowance elsewhere. For example the (6) at Clay Cross North being a case in point. That train is going to stop but has a passing time at the junction if there was a conflict, which there isn't. Without looking at it properly it is an odd one as it just looks like it will sit time at Chesterfield.

 

[Tomnick]

That looks genuine, as you have got other chunks of allowance elsewhere. For example the (6) at Clay Cross North being a case in point. That train is going to stop but has a passing time at the junction if there was a conflict, which there isn't. Without looking at it properly it is an odd one as it just looks like it will sit time at Chesterfield.

It's the unadvertised stops at Beeston, Attenborough and Long Eaton that perplex me. Wouldn't pathing time approaching wherever the conflict is be more appropriate?

 

[Wilts Wanderer]

There’s two schools of thought regarding restart allowances (the post-pathing running time adjustment mentioned.)

If the headway is 4 mins and you’ve got 3 or 4 aspect signalling at a converging junction, with two trains presenting naturally at the same time, the second to pass the junction will have (4) minutes pathing allowance. In practice, train 2 will pass the junction probably only 2 mins behind train 1, on a restrictive signal aspect but effectively early, and then has 2 mins in hand to accelerate and regain linespeed and booked time on the 4 min headway.

This fact is probably why the daily national timetable doesn’t fall over due to pathing allowances. However in my experience it doesn’t quite work in the following circumstances
- very high linespeed
- tight headways
- second train is a freight
- lots of timing points close together

The combination of these on parts of the GWML is why the Western has the table of restart allowances I believe. They only really need applying where linespeeds exceed 100mph.

It's the unadvertised stops at Beeston, Attenborough and Long Eaton that perplex me. Wouldn't pathing time approaching wherever the conflict is be more appropriate?

Increasingly ARS is unable to account for pathing time when regulating trains at junctions. It’s a serious flaw with the technology and one reason why traffic management systems are desperately needed (and installing ARS as standard with new resignalling schemes isn’t always the best answer.)

Edit: So to add, looking at the train in question, I suspect that the resignalling at Derby has added ‘vanilla’ ARS and NR’s planners have been told not to apply more than token pathing allowances approaching the station area to reduce the risk of mis-regulation of early running trains. That has manifested itself as a nonsensical path and doesn’t actually solve the problem if the train doesn’t stop at those stations!

 

[Peregrine 4903]

Yeah ARS causes serious issues with pathing time. Its specifically advised to try and avoid adding pathing time especially approaching junctions in ARS areas as there is a good chance that ARS will just regulate the train that turn up first and send them in the wrong order causing an unessecary delay. However its often unavoidable though and often is the only way to get the timetable to work.

There is a constant debate about whether adding pathing time or dwells is best best way to regulate services. The issue with dwells is that if you add dwells to passenger services at junction, there almost always won't be an SRT for it which means either you have to TRT the train or unless an SRT is requested the train can't be published.

 

[jfollows]

you have to TRT the train

An interesting discussion going on here: could you please explain this particular point though because I'm baffled? Thank you!

 

[Wilts Wanderer]

Yeah ARS causes serious issues with pathing time. Its specifically advised to try and avoid adding pathing time especially approaching junctions in ARS areas as there is a good chance that ARS will just regulate the train that turn up first and send them in the wrong order causing an unessecary delay. However its often unavoidable though and often is the only way to get the timetable to work.

There is a constant debate about whether adding pathing time or dwells is best best way to regulate services. The issue with dwells is that if you add dwells to passenger services at junction, there almost always won't be an SRT for it which means either you have to TRT the train or unless an SRT is requested the train can't be published.

It is avoidable, in that at specific locations ARS has to be designed to only attempt to route a train a maximum of 2 mins before it’s booked time, as an alternative to the ‘muddle through and provide 2 greens for everything’ of standard ARS routing. However individual signals can’t have mixed settings, so it’s all or nothing, plus it has to be specced at the design stage, which timetabling functions don’t normally get involved with (although various people are pressing for this to be improved.) Also it needs a good advance understanding of what the post-remodelling timetable structure will be, which isn’t always possible particularly given NR’s recent record of deferring major timetable change due to internal resource constraints.

Personally, without traffic management (such as Luminate on the Western, which is excellent from all accounts), I think the wider application of ARS is foolish and a result of the badly though through ROC strategy which requires it. Someone - a signaller - once said that having ARS is like working with the worst trainee signaller ever - it just makes the same preventable mistakes again and again, day after day.