Speed limits

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Inversnecky

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I’m aware that a train is not allowed to accelerate to a higher speed until the last wagon/carriage has passed the notice.

My question is, how does the driver know that’s happened? Looking back/cameras/knowledge of train length and judging? Has the method change with technology?

Also, the speed limit being the max permissible line speed, do trains ever exceed that somewhat (eg to catch up time), or always have to be under it?

(Obviously talking about main line running, and not on pointwork, etc.)
 
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Dieseldriver

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Generally it is down to experience/route/traction knowledge to know when you’re clear of a lower speed restriction. With modern freight locomotives there is a train length switch. You input the length of the train onto the computer and when your cab passes a speed restriction sign for a higher speed, you press the train length button which starts a countdown and sounds a noise when the rear of your train is clear.
Speeding is not allowed full stop.
 

Egg Centric

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Also - note that on the London Underground, because all the trains are the same length, they actually put the signs such that the speed limit applies when the front of the train passes the sign.
 

40129

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Also - note that on the London Underground, because all the trains are the same length, they actually put the signs such that the speed limit applies when the front of the train passes the sign.
So how does this work with S stock as IIRC this comes in three different lengths - 6, 7 and 8-car - various combinations of which share sections of line. especially the north and south sides of the Circle line. Similarly, are District and Piccadilly or Metropolitan and Piccadilly line trains the same length (metres not cars) as they share tracks between Hammersmith and Ealing Common and between Rayners Lane and Uxbridge respectively
 

Egg Centric

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So how does this work with S stock as IIRC this comes in three different lengths - 6, 7 and 8-car - various combinations of which share sections of line. especially the north and south sides of the Circle line. Similarly, are District and Piccadilly or Metropolitan and Piccadilly line trains the same length (metres not cars) as they share tracks between Hammersmith and Ealing Common and between Rayners Lane and Uxbridge respectively

Common sense suggests they would just use the worst case - but I don't actually know this!
 

Domh245

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So how does this work with S stock as IIRC this comes in three different lengths - 6, 7 and 8-car - various combinations of which share sections of line. especially the north and south sides of the Circle line. Similarly, are District and Piccadilly or Metropolitan and Piccadilly line trains the same length (metres not cars) as they share tracks between Hammersmith and Ealing Common and between Rayners Lane and Uxbridge respectively

S stock only comes in 7s and 8s, and the only commonly overlapped section is Baker Street - Aldgate (Some S7s go over the metropolitan to Neasden for maintenance work there but obviously these are all designed around the 8 car units anyway). I'm fairly certain that over that common section they were just placed at the nominal 8 car clear point, although I also want to say that this area has now (mostly?) been moved over to ATO/CBTC making it irrelevant!
 

Bald Rick

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Speeding is strictly not allowed, unless in tightly controlled test conditions, with relevant notices posted to all applicable staff in advance.

That doesn’t stop it happening, mind. There have been some interesting speeds done by class 80x on the ECML recently.
 

Inversnecky

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Speeding is strictly not allowed, unless in tightly controlled test conditions, with relevant notices posted to all applicable staff in advance.

That doesn’t stop it happening, mind. There have been some interesting speeds done by class 80x on the ECML recently.

How come delays can sometimes be "made up", if speeding isn't allowed and drivers are expected to go at line speed?
 

Ceat0908

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How come delays can sometimes be "made up", if speeding isn't allowed and drivers are expected to go at line speed?
Recovery time built into timetables, efficient station stops, harsher breaking and quicker acceleration.
 

172007

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Network Rail LNW have a notice In the current WON about trialling "A" boards instead of "T"boards at TSR's where "T" stands for acceleration point.

I hope a few more trials are done as we have a TSW for a foot crossing where it does not matter about the speed through the TSR but rather how quick it takes for a train to arrive at the foot crossing to give user's a chance to cross safely after starting to cross with no train in sight.
 

dk1

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Double step on the DSD pedal gives us an audible warning when the train is clear now but I find the loud bleeps annoying so prefer to use my experience.
 

Bald Rick

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I hope a few more trials are done as we have a TSW for a foot crossing where it does not matter about the speed through the TSR but rather how quick it takes for a train to arrive at the foot crossing to give user's a chance to cross safely after starting to cross with no train in sight.

That can be solved in other ways:

1) by placing the TSR T board one train length ahead of the level crossing on approach. Of course it needs to be set for the shortest train likely to use the route, but it makes a big difference

2) putting an appropriate comment next to the TSR in the Weekly Opersting Notice (“Drivers may commence acceleration back to linespeed as soon as the front cab has passed the T board”)

Both have been done before. Driver Stsndsrds people tend to prefer 1)
 

dk1

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I'm not sure why at for example level crossings with temporary speed restrictions the A is not more widely used at Termination boards. After all the speed you approach the crossing is the important bit & acceleration can then start immediately.
 

theageofthetra

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Some speed limits are to do with signal sighting rather than a physical limitation of the track. For those what is the point of waiting for all 12 coaches to be clear?
 

dk1

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Some speed limits are to do with signal sighting rather than a physical limitation of the track. For those what is the point of waiting for all 12 coaches to be clear?
Exactly hence the 'A' on the 'T' board. Before that I recall the WON mentioning Gamekeepers crossing on the East Suffolk Line that had a 20mph TSR that drivers may accelerate immediate once reaching the T board.
 

edwin_m

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Exactly hence the 'A' on the 'T' board. Before that I recall the WON mentioning Gamekeepers crossing on the East Suffolk Line that had a 20mph TSR that drivers may accelerate immediate once reaching the T board.
Doesn't this apply to all AOCL/ABCL restrictions?
 

Re 4/4

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My question is, how does the driver know that’s happened? Looking back/cameras/knowledge of train length and judging? Has the method change with technology?

In 2010, a glacier express derailed in Fiesch, Switzerland causing one death and 42 injured - the accident report established that the driver started accelerating when the head rather than the end of the train passed the end of a permanent restriction for a severe curve.

There didn't seem to be any technology involved, just the driver's judgement and route knowledge.
 

hexagon789

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do trains ever exceed that somewhat (eg to catch up time), or always have to be under it?
Historically it did happen, not that infrequently, nowadays only by accident really (the TPE 802 doing over 140mph a wee while back being a case in point).

They do download the OTDR logs from time-to-time to check.
 

cambsy

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As Hexagon 789 said, now days, drivers dont speed to make up time, most seem to get is 2-3mph over limit, ie on a 125mph line, one might see 127-128mph max, down hill maybe 129, this because drivers get checked for speeding etc, un like in the old days where speeds 10 mph over limit were not un common, seen logs of Deltics doing 110mph plus, HST’s doing 135mph and 91’s doing 135-138mph, I have done 135mph plus on 91’s in the 90’s.
 

hexagon789

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As Hexagon 789 said, now days, drivers dont speed to make up time, most seem to get is 2-3mph over limit, ie on a 125mph line, one might see 127-128mph max, down hill maybe 129, this because drivers get checked for speeding etc, un like in the old days where speeds 10 mph over limit were not un common, seen logs of Deltics doing 110mph plus, HST’s doing 135mph and 91’s doing 135-138mph, I have done 135mph plus on 91’s in the 90’s.
I've seen a good log of a Leeds-KX Deltic+8 making up an 11 min late start from Doncaster with sustained 110mph+ running including touching 114 and 115mph during the journey.

HSTs of course ran often enough at 130/135mph+ on the WR within the first 18 months before speed limiters were fitted and there are numerous reports of speeds approaching and exceeding 140 being obtained as well.
 

Kraken

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I’m sure there’s an extremely simple answer to this question but why are trains even capable of exceeding the maximum speed they will encounter in the UK? Why doesn’t an HST just cut power at 125mph like the speed limiter in a car?
 

MrEd

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I’m sure there’s an extremely simple answer to this question but why are trains even capable of exceeding the maximum speed they will encounter in the UK? Why doesn’t an HST just cut power at 125mph like the speed limiter in a car?
They do nowadays- I believe HSTs have a device fitted which cuts traction power at around 128mph, and have had this fitted since the 1980s. I think it’s set at 128mph so as to take into account speedometer variations.
 

hexagon789

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I’m sure there’s an extremely simple answer to this question but why are trains even capable of exceeding the maximum speed they will encounter in the UK? Why doesn’t an HST just cut power at 125mph like the speed limiter in a car?
Generally speaking they test trains to a 10% overspeed, obviously they could then impose a strict maximum service speed and many modern classes do but the technology was basic and probably not considered a worthwhile expenditure back then. The HSTs only gained their speed limiters after 18 months in traffic because drivers were taking then up to 130-135mph and more sometimes, so they fitted limiters to impose a 132mph maximum. That gave a comfortable threshold for drivers to run at 125 allowing for different people reading the speedos slightly differently as well and so forth

They do nowadays- I believe HSTs have a device fitted which cuts traction power at around 128mph, and have had this fitted since the 1980s. I think it’s set at 128mph so as to take into account speedometer variations.
It's 132mph, albeit on power cars with the original WSP system it doesn't account for wheel wear, so at minimum diameter it actually cuts in at about 123mph on those PCs
 

Kraken

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Lovely, thanks MrEd and Hexagon for the clarification. I guess it makes sense to have a small amount of leeway built into such systems.
 

hexagon789

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Lovely, thanks MrEd and Hexagon for the clarification. I guess it makes sense to have a small amount of leeway built into such systems.
Another example is the Automatic Train Protection fitted on the GWML this has 3 braking curves -

The speed curve
The warning curve
The intervention curve

The first is the current permitted speed
The second is 3 mph above that at which point a warning sound goes off
The third is 6mph above the permitted speed and if that is crossed the ATP system will then make a full service brake application.

Again the reason for the three curves is to allow the driver a bit of leeway in controlling the speed of their train.
 

43066

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They do nowadays

In many cases they don’t, even on types far newer than the HST. It’s down to the driver to avoid exceeding max line speed, just as with any other speed limit.

I’m sure there’s an extremely simple answer to this question but why are trains even capable of exceeding the maximum speed they will encounter in the UK? Why doesn’t an HST just cut power at 125mph like the speed limiter in a car?

I’ve certainly never driven a car with a 70mph speed limiter.
 
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