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Speed limits

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Kraken

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

Sorry I didn’t specify. Some cars have a thing where you can set a certain speed and when you reach that speed the power will cut off regardless of how much throttle you are giving. A bit like cruise control but you still accelerate and brake like normal.
 

SteveyBee131

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Sorry I didn’t specify. Some cars have a thing where you can set a certain speed and when you reach that speed the power will cut off regardless of how much throttle you are giving. A bit like cruise control but you still accelerate and brake like normal.
Ah, like a speed-set. The 90s and 91s have one, don't know if any others do
 

dk1

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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?
Been common for many years. Class 90s/DVTs had ASL in 1987 and class 170s had limiters kicking in at 102mph from the late 90s.
 

Ben Bow

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In answer to the original question about how does the driver know when the rear of the train is clear of the speed (or 'T') board, at least class 66's have the option to input the train length (as shown on the TOPS consist printout) into the QTron (I think it was) at the start of the journey. Then, when en route and the loco passed a speed board, a countdown button could be operated which then counted down until the rear of the train was clear, 10% was added to the input length for extra safety. I expect other modern locomotives have a similar feature?
 

43066

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Sorry I didn’t specify. Some cars have a thing where you can set a certain speed and when you reach that speed the power will cut off regardless of how much throttle you are giving. A bit like cruise control but you still accelerate and brake like normal.

Ah yes, I know what you mean. I’ve driven cars with that, I’ve just never used it ;).

Ah, like a speed-set. The 90s and 91s have one, don't know if any others do

Speed set was on the EMUs I used to sign but was not permitted to be used and/or deactivated (depending on who you asked).

Until we move to full ETCS speed controlled signalling there’s little point in speed limiters set at line speed. Drivers are hardly likely to speed deliberately, and the most dangerous limits to exceed will be ESRs and TSRs far below line speed.
 

Bald Rick

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Am I right in thinking they're 200km/h or off? Whereas the 90s and 91s are variable in 5m/h increments.

Not sure, but don’t think so - as the RAIB report into the Neville Hill collision implies it could have been used there, at a speed clearly less than 125mph. (Ironically, see the avatar of @43066 for the result!)
 

hexagon789

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Ah, like a speed-set. The 90s and 91s have one, don't know if any others do
And the 89, the unique 87101, 175s, 180s, 185s, 390s and a few more

Am I right in thinking they're 200km/h or off? Whereas the 90s and 91s are variable in 5m/h increments.
I did read something about the 80x ASL, something like it only works at 60mph or above and works in km/h so the maximum it will allow is 124mph.

I think, I may be mis-remembering bits
 

dgl

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Ah yes, I know what you mean. I’ve driven cars with that, I’ve just never used it ;).
it's fun when you activate it un-knowingly, my sister has done that twice and once was in a loan car, she got a bit worried when it would not accelerate past a really low speed (~15Mph?), disabled it an all was well.
 

JonasB

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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.
But apart from checking the logs, is there no system to prevent speeding?
 

craigybagel

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And the 89, the unique 87101, 175s, 180s, 185s, 390s and a few more
Though as far as I know it's long since disabled on the 175s - judging by the state of some of the buttons I'm not sure they've ever worked.

The ERTMS 158s have a speed limiter even when running on level 0 (ie when running on conventional signals). If you go much above 90 the speedometer turns orange and starts beeping. At a higher speed the brakes will apply, bringing the train back down to 90.

When the cab is being set up, you have the option of telling the system if a 75mph unit is attached, in which case the speed limits are lowered accordingly.
 

ComUtoR

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Not sure, but don’t think so - as the RAIB report into the Neville Hill collision implies it could have been used there, at a speed clearly less than 125mph. (Ironically, see the avatar of @43066 for the result!)

Here is where I tend to find the RAIB a little toothless. A TOC may have the capability to implement use of a speed limiter to prevent a Neville Hill style collision but can freely refuse to do so. My TOC doesn't allow the use of Speed Set.
 

AM9

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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’ve certainly never driven a car with a 70mph speed limiter.
My last car had a cruise/limiter which could be set to any speed between 20mph and 75mph. It had a CVT gearbox as well so it could reduce the (virtual) gear to provide engine braking if necessary.
 

43066

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My last car had a cruise/limiter which could be set to any speed between 20mph and 75mph. It had a CVT gearbox as well so it could reduce the (virtual) gear to provide engine braking if necessary.

A Japanese car; with a CVT gearbox. Ouch. That sounds like an (automotive) fate worse than death.
 

Eccles1983

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175's has an overspeed cut out.

The overspeed will flash at about 102mph, I think at 105mph it cuts the power.

It flashes like mad in leaf fall.
 

plugwash

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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?
The timing rules used for timetables do not assume everything will go perfectly, they have slack built in.

Also many timetables are scheduled based on slower rolling stock than that which normally operates the line. While the top speed may not be any higher due to linespeed restrictions a modern EMU like a 331 running on timings intended for an older EMU like a 319 can make up a lot of time due to faster acceleration.

Also if things aren't too busy station stops can often be completed in less time than scheduled.
 

43096

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Here is where I tend to find the RAIB a little toothless. A TOC may have the capability to implement use of a speed limiter to prevent a Neville Hill style collision but can freely refuse to do so. My TOC doesn't allow the use of Speed Set.
I think you’re misunderstanding what the purpose of the RAIB is. It’s remit is to investigate, report and recommend. It isn’t there to take enforcement action, that is down to others, notably the ORR.
 

StationTown

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id read something about the 80x ASL, something like it only works at 60mph or above and works in km/h so the maximum it will allow is 124mph.

I think, I may be mis-remembering bits

No, this is not the case. The 80x ASL can be set at any speed or none. The only exception is when an 801 unit is running in diesel/limited traction mode. In this instance the ASL will not operate.
 

TheEdge

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Speed set in the 745/755s is set up in such a way that you have to set it to even move. It can't be turned off or set to 0 and when you open the desk it sets to 1mph by default.
 
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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?
Most timetables are based on sectional running times, which are based on recorded data. This usually will be assigned to rolling stock which is either similar or the same as what usually works the route. Note, if a train loses time due to performance differentials (e.g. a 150 on a 158 diagram) then this would be considered a fleet delay rather than a timetabling problem.
Added into the timetables are engineering allowances to cover speed restrictions imposed, pathing allowances to allow trains to change routes for example, or running against expected restricted aspects and performance allowances which are agreed as a measure to protect against services persistently losing time in a section. TOCs usually are reluctant to include the latter as this will negatively impacts the business.

So, if a train loses time in a section and it has 1.5 mins performance allowance, it may catch that time up. It is more difficult to catch up with engineering and pathing allowances. Not impossible but more difficult.

A signalman can also proactively path a train to allow it to catch up time and prevent a PPM failure. This will usually be agreed as part of a regulation policy. It may mean holding other services to let a train catch up to its schedule and prevent it being regulated for trains which are on time.

I hope this gives an overview of how delays can be caught up. Unfortunately, the railway is very tightly pathed and trains run very close together, it can be extremely challenging to catch up time.

I was on a TGV in France a number of years ago. We left the regional station I was travelling from 1h45 late but arrived into Paris only 45 late. I strongly suspect we exceeded the speed limit to do this when we were on the LGV as there would have been very little traffic ahead of us, but it was a very long time ago and I have no evidence we did as smart phones weren't a thing then.
 

SteveM70

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Slightly off topic but apropos limiters in cars, the most effective - and cheapest - I’ve encountered was a “rent a wreck” cheap hire car in New Zealand which had a bell somewhere in the depths of the dashboard that went off whenever you went over the limit that was set (60mph I think). Ding! Ding! Ding! Every second. The aural version of Chinese water torture
 

traingeek97

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How is a train’s speed recorded/monitored to ensure a driver isn’t speeding? I remember seeing an old episode of The Tube where a Driver Manager was standing on a platform with a speed gun. Does that still happen? Are there cameras like on roads?
 

Jamiescott1

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How are speed limits decided?
For example, leaving Marylebone - once out of the tunnels the line is straight but the speed limit is less than 100 until the line reaches Wembley. Why can't it be 100 sooner?
 

driver9000

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How is a train’s speed recorded/monitored to ensure a driver isn’t speeding? I remember seeing an old episode of The Tube where a Driver Manager was standing on a platform with a speed gun. Does that still happen? Are there cameras like on roads?

Data recorders can be downloaded and are routinely screened as part of a Driver's assessment cycle. Some Hot Axle detectors have speed equipment built into them which can show the speed of passing trains in the signal box. Radar traps are less common now that all trains have OTDR equipment fitted.
 

GB

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How is a train’s speed recorded/monitored to ensure a driver isn’t speeding? I remember seeing an old episode of The Tube where a Driver Manager was standing on a platform with a speed gun. Does that still happen? Are there cameras like on roads?
Speed guns are very rare these days but can still be used.
Modern stock or retrofitted stock can have the ability for real time monitoring and send the results straight to mangers laptop.
Random OTMR downloads or downloads after and incident.
Driver‘s professionalism and risk of disciplinary action or having an incident.

There isn’t really anything to stop a driver doing 55 in a 50 for example tho...other than the driver hopefully thinking about some of the above.
 

Bald Rick

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How are speed limits decided?
For example, leaving Marylebone - once out of the tunnels the line is straight but the speed limit is less than 100 until the line reaches Wembley. Why can't it be 100 sooner?

That’s a big subject, not for this thread. Essentially it comes down to around 100 potential factors relating to track, signalling, structures, clearances, level crossings, electrification (not in the case of the Chiltern line, obviously), stations, maintenance standards, rolling stock capability and operability. Straightness of track is but one of those factors.
 

The Planner

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The timing rules used for timetables do not assume everything will go perfectly, they have slack built in.

Also many timetables are scheduled based on slower rolling stock than that which normally operates the line. While the top speed may not be any higher due to linespeed restrictions a modern EMU like a 331 running on timings intended for an older EMU like a 319 can make up a lot of time due to faster acceleration.

Also if things aren't too busy station stops can often be completed in less time than scheduled.

Most timetables are based on sectional running times, which are based on recorded data. This usually will be assigned to rolling stock which is either similar or the same as what usually works the route. Note, if a train loses time due to performance differentials (e.g. a 150 on a 158 diagram) then this would be considered a fleet delay rather than a timetabling problem.
Added into the timetables are engineering allowances to cover speed restrictions imposed, pathing allowances to allow trains to change routes for example, or running against expected restricted aspects and performance allowances which are agreed as a measure to protect against services persistently losing time in a section. TOCs usually are reluctant to include the latter as this will negatively impacts the business.

So, if a train loses time in a section and it has 1.5 mins performance allowance, it may catch that time up. It is more difficult to catch up with engineering and pathing allowances. Not impossible but more difficult.

A signalman can also proactively path a train to allow it to catch up time and prevent a PPM failure. This will usually be agreed as part of a regulation policy. It may mean holding other services to let a train catch up to its schedule and prevent it being regulated for trains which are on time.

I hope this gives an overview of how delays can be caught up. Unfortunately, the railway is very tightly pathed and trains run very close together, it can be extremely challenging to catch up time.

I was on a TGV in France a number of years ago. We left the regional station I was travelling from 1h45 late but arrived into Paris only 45 late. I strongly suspect we exceeded the speed limit to do this when we were on the LGV as there would have been very little traffic ahead of us, but it was a very long time ago and I have no evidence we did as smart phones weren't a thing then.
Also bear in mind running times are based on ½ minutes and therefore rounded, it shouldn't make much difference end to end, but some roundings will allow time to be caught up.
In terms of allowances, again, there is rounding in there so some will be higher than others. Engineering allowance (box time) is actually the easiest way of making time up as no TSRs means several minutes can be caught up, allowances for approach control/slow speed diverging shouldn't really give you much. If you are running late then the train in front of you that required pathing allowance to be put in is likely not where it is meant to be, so more easy minutes to claw back.
Performance allowance is completely TOC based, they bid for that and add it, it isn't imposed by NR and is "padding" in the truest sense.
 
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