Speed limits and making up time

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Scott M

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I have been reading that speed limits are often limited by factors such as passenger comfort before being limited by risk of derailment (ie the board may say 90mph but you could do 100mph without running the risk of derailing).

With this in mind I was wondering:

A) How far above the speed limit can you go before running the risk of a derailment - 5mph, 10mph, 20mph etc? I know it will likely vary in different places but whenever there is variation there is an average.

B) Can drivers be a bit generous with their interpretation of the speed limit in order to make up lost time at the expense of passenger comfort?
 
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t_star2001uk

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I was always taught that line speed is set in stone. Anything up to the permitted speed belongs.to me, signalling allowing of course. Anything over the permitted speed carries a potential interview without coffee and biscuits. So no we cannot exceed the permitted speed.
 

Mintona

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I'm not sure how you could 'interpret' a fixed number in any way other than not go over it.
 

AM9

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I have been reading that speed limits are often limited by factors such as passenger comfort before being limited by risk of derailment (ie the board may say 90mph but you could do 100mph without running the risk of derailing).

Maximum speed limits arerequired for many more reasons than stability/comfort on curves, e.g.

track/infrastructure condition
local neighbourliness
signal spacing/approach control
passengers on platform considerations
 

edwin_m

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If the speed restriction is solely due to curvature then the train could go a lot faster round the curve without derailing. However, "passenger comfort" is perhaps an oversimplification as passenger safety would be at risk even well below the derailing speed, from things like standees falling sideways and passengers being scalded by hot coffee. As pointed out above there are all sorts of reasons for a speed restriction - about 80 possible ones I believe - so something else could go wrong too.
 

SpacePhoenix

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Do drivers get a couple of mph leeway/grace over the speed limit. I'd be surprised if no driver never ever went even .5mph over speed limits
 

pdeaves

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In practical terms, no, there is no 'grace'. If there was, there would be perennial arguments over interpretation. The rules are the rules and drivers are expected to comply. The turning of blind eyes, so prevalent on our road system, does not happen on the railways. If only the roads were regulated as well as the railways...
 

DY444

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In practical terms, no, there is no 'grace'. If there was, there would be perennial arguments over interpretation. The rules are the rules and drivers are expected to comply. The turning of blind eyes, so prevalent on our road system, does not happen on the railways. If only the roads were regulated as well as the railways...

The "turning of a blind eye" doesn't happen now on the railways but it did frequently once upon a time. REPs over the ton down the hill to Winchester, 47s on the ECML doing crazy speeds when substituting for deltics on the D280 turns, the Old Oak Common 130 club, and countless others.
 

ainsworth74

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The "turning of a blind eye" doesn't happen now on the railways but it did frequently once upon a time. REPs over the ton down the hill to Winchester, 47s on the ECML doing crazy speeds when substituting for deltics on the D280 turns, the Old Oak Common 130 club, and countless others.

I thought it was the 140 club! :lol:
 

MisterT

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I don't know for the UK, but I was told during my driver training in the Netherlands that the technical limit is usually two times the actual speed limit (of course there are many exceptions).
We have had a few incidents in the past where a train driver had been driving around 90 kmh over a 40 kmh set of points without any derailment or damage to the tracks and the train.
 

colchesterken

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I was on the TGV a few weeks ago the information screen, showed the train speed over a set point it seemed to click in at about 240 kph
It was interesting to watch never touched 300. 294 -296 but no more it that because the driver did not want to trip the on train monitoring equipment
 

MonsooN

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I remember hearing an interview on the radio with someone senior from the DfT shortly after that awful derailment in Spain which was caused by the driver going too fast.

They said that that could never happen in the UK because the train speed is electronically controlled (at least on some lines) The drivers have a 2 MPH leeway, so an HST can go up to 127MPH, another 2 MPH beyond that and the system will automatically apply the brakes, so that would mean the max speed is theoretically 128.9 mph before the brakes get automatically applied.*

I thought drivers could exceed the limit fractionally to make up time if they are a couple of minutes behind schedule. I take it from the posts above that this ins't the case?

*I did hear this interview a couple of years ago, so I may not have recalled the details exactly.
 
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Bromley boy

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I remember hearing an interview on the radio with someone senior from the DfT shortly after that awful derailment in Spain which was caused by the driver going too fast.

They said that that could never happen in the UK because the train speed is electronically controlled (at least on some lines) The drivers have a 2 MPH leeway, so an HST can go up to 127MPH, another 2 MPH beyond that and the system will automatically apply the brakes, so that would mean the max speed is theoretically 128.9 mph before the brakes get automatically applied.*

I thought drivers could exceed the limit fractionally to make up time if they are a couple of minutes behind schedule. I take it from the posts above that this ins't the case?

*I did hear this interview a couple of years ago, so I may not have recalled the details exactly.

In practice you may momentarily forget/brake a little late and perhaps enter a speed at +5mph. My DI assures me this is not a big deal so long as it is a small difference and quickly rectified.

There's absolutely no flexibility to exceed the speed limit to "make up time". If it was noticed on a download that you were regularly exceeding the speed limit you would be hauled up about it and retrained/disciplined.

I'm sure in practice there is a good deal of safety margin built into the speed limits set before anything as catastrophic as a derailment would occur, for obvious reasons.
 

ainsworth74

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I thought drivers could exceed the limit fractionally to make up time if they are a couple of minutes behind schedule. I take it from the posts above that this ins't the case?

Maybe in the 'good' old days but not anymore.
 

tsr

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This is not to be confused with "eco-driving" (or similar) policies, which may recommend a given range of speeds which are lower than the actual linespeed over a section of track. Sometimes these policies, as well as general timekeeping, are aided by a Driver Advisory System (DAS), which is generally an additional screen or function on the cab control desk/dashboard which advises the desirable speed at which the computer believes the train should travel. The clue regarding that is in the name: "Advisory". It can even be turned off at times per technical requirements - and if the recommendation is unsafe per the conditions, or too restrictive per the timetable, the driver can drive purely in line with their rules, traction and route knowledge.

The upshot of all this is that a service which is able to keep to time at a lower speed than the permissible linespeed on one day, when it is running on time, may seem to be going faster and "making up time" on the next day when it is running late. A driver may be recommended by an advisory system, or required by policy, to usually drive in a certain way; but, in fact, the previous day may have seen the train being driven per the policies, but the second day may have seen those policies overridden by the train being pushed to peak performance and taking advantage of driving closer to the permitted linespeed - where signal aspects permitted it. A good DAS (I await drivers' comments, which may be amusing...) should also display a higher speed if this is possible in accordance with said linespeed. Naturally I am not condoning dangerous practices of trying to second-guess the signal aspects ahead (running a safe system of work on the basis of assumptions is always bad) but there are ways to try to make up time which can result in a feeling of a quicker journey between two points on different days.
 
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Muzer

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I remember hearing an interview on the radio with someone senior from the DfT shortly after that awful derailment in Spain which was caused by the driver going too fast.

They said that that could never happen in the UK because the train speed is electronically controlled (at least on some lines) The drivers have a 2 MPH leeway, so an HST can go up to 127MPH, another 2 MPH beyond that and the system will automatically apply the brakes, so that would mean the max speed is theoretically 128.9 mph before the brakes get automatically applied.*

I thought drivers could exceed the limit fractionally to make up time if they are a couple of minutes behind schedule. I take it from the posts above that this ins't the case?

*I did hear this interview a couple of years ago, so I may not have recalled the details exactly.
This only applies to lines with ATP (parts of the Great Western and Chiltern main lines), TASS (the West Coast Main Line), and ETCS (currently only the Cambrian Coast line in passenger service). On other lines, speed is only spot-checked (by a basic system called TPWS) on the approaches to signals at danger/caution protecting things other than a rear-end collision (eg signals for junctions or (I think) level crossings), and on the approaches to particularly severe speed restrictions.

But the speed is recorded by the OTDR the whole time against some way of determining the location, and so managers can determine whether or not a driver was speeding at a given time, and they can and do do random downloads to check it.


(Acronyms: ATP: Automatic Train Protection. TASS: Tilt Authorisation and Speed Supervision. ETCS: European Train Control System. TPWS: Train Protection and Warning System. OTDR: On-train Data Recorder (equivalent to a black box))
 
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Johncleesefan

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I'm not sure how atp works as I don't work trains equipped with it but in mine the way you will be caught is either tpws grids ir otdr downloads. I drive exactly the same if I'm early, ob time late or upside down. If I'm 2 mins late leaving terminus, chances are I will be 2 mins late the whole journey unless generous station dwell time is in my diagram. Too risky to chance an extra 5mph. Not for me
 

rebmcr

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Do any signalling systems record the average speed of trains between (for example) two track circuit sections?
 

philthetube

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I seem to recall hearing somewhere that when HS1 was being built it the track had to be tested at 25% above line speed, though I cannot see how that could be achieved, unless this was just points and any other non straight rail sections.
 

Elecman

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Do any signalling systems record the average speed of trains between (for example) two track circuit sections?

Certainly 30+ years ago Preston PSB did have a section of track that printed out each trains speed over it, I assume Carlisle and Warrington PSBs also did as they were of the same vintage and design.
 

edwin_m

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I remember hearing an interview on the radio with someone senior from the DfT shortly after that awful derailment in Spain which was caused by the driver going too fast.

They said that that could never happen in the UK because the train speed is electronically controlled (at least on some lines) The drivers have a 2 MPH leeway, so an HST can go up to 127MPH, another 2 MPH beyond that and the system will automatically apply the brakes, so that would mean the max speed is theoretically 128.9 mph before the brakes get automatically applied.*

They had a similar system in Spain to prevent overspeed on the high speed line. However where the derailment happened was just off the end of the high speed line so the speed wasn't enforced. One hopes that has now been fixed there and anywhere else in Europe where the same applied.

The fatal TGV accident in France last autumn was also just off the end of the high speed line proper, on a lower-speed curve joining it back into the older main line. I believe the speed supervision was provided for this curve, but this was a test train at 10% overspeed, which could only be done by taking the speed supervision out of use.

Both accidents demonstrate how at that sort of speed a small lapse of concentration on the approach to a speed reduction can be catastrophic, as would the failure to slow down for a train in front. One reason why ATP systems are universal on high speed routes.
 

Phil.

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I thought it was the 140 club! :lol:

Not sure about that but there was the twenty minute club - as in twenty minutes from Paddington to Reading. But that was before boy managers came along and when drivers could be trusted on their judgement.
 

QueensCurve

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I have been reading that speed limits are often limited by factors such as passenger comfort before being limited by risk of derailment (ie the board may say 90mph but you could do 100mph without running the risk of derailing).

With this in mind I was wondering:

A) How far above the speed limit can you go before running the risk of a derailment - 5mph, 10mph, 20mph etc? I know it will likely vary in different places but whenever there is variation there is an average

The track is "canted" (outer rail higher on the curve) to keep passenger comfort when the train rounds the curve at speed. Speed limits are set at a particular "cant deficiency" based on passenger comfort.

Maximum cant deficiencies in Britain are historically lower than in other European countries. I believe there was some relaxation of allowable cant deficiencies on the WCML about 30y ago to shave a few minutes of the journey time.

Research by the BRB in the 1960s identified that, with a certain conicity on the wheel profile and lateral suspension, trains could go 40% faster than speed limits based on cant deficiency without risk of derailment.

The APT was developed to tilt up to 9 degrees to compensate 100% for cant deficiency to allow the train to go 40% faster round the bend while keeping passenger comfort.

Todays tilting trains don't compensate for 100% of cant deficiency, only about 80% because this was found more comfortable for passengers.

In today's safety climate t would no doubt be unacceptable for drivers to exceed speed limits. In the early 1980s I recall clocking trains at 110mph descending Shap bank when the speed limit was 100.
 

Senex

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Maximum cant deficiencies in Britain are historically lower than in other European countries. I believe there was some relaxation of allowable cant deficiencies on the WCML about 30y ago to shave a few minutes of the journey time.
And the MML too, so, for example, the curve at Wigston went up from 70 to 80. IIRC the permissible cant deficiency went up from 130 mm to 150 mm if various conditions (no S&C, proper transitions etc) could be met.

These were both LMR examples. Did the same happen in other Regions? For example, was this when (and why) the Hele/Cullompton curves north of Exeter went up?
 

DarloRich

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I have been reading that speed limits are often limited by factors such as passenger comfort before being limited by risk of derailment (ie the board may say 90mph but you could do 100mph without running the risk of derailing).

With this in mind I was wondering:

A) How far above the speed limit can you go before running the risk of a derailment - 5mph, 10mph, 20mph etc? I know it will likely vary in different places but whenever there is variation there is an average.

B) Can drivers be a bit generous with their interpretation of the speed limit in order to make up lost time at the expense of passenger comfort?

Surely the speed limit isn't open to interpretation. If it says 90 the maximum speed you can travel is 90. I am sure drivers know where they can make up time within the provided envelope.
 

t_star2001uk

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I'm not sure how atp works as I don't work trains equipped with it but in mine the way you will be caught is either tpws grids ir otdr downloads. I drive exactly the same if I'm early, ob time late or upside down. If I'm 2 mins late leaving terminus, chances are I will be 2 mins late the whole journey unless generous station dwell time is in my diagram. Too risky to chance an extra 5mph. Not for me

As far as i can remember (I did ATP training in 1997), ATP gives a warning of 3 MPH overspeed and will then intervene at 6 mph overspeed. Class 68's have a Traction Cutout which operates at 102mph and does not allow power to be retaken until the speed drops to at least 95mph.
 

QueensCurve

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As far as i can remember (I did ATP training in 1997), ATP gives a warning of 3 MPH overspeed and will then intervene at 6 mph overspeed. Class 68's have a Traction Cutout which operates at 102mph and does not allow power to be retaken until the speed drops to at least 95mph.

Classic DMUs had a similar cutout that cut the power at above 68mph. If a driver allowed this to cut in he would lose speed/time in consequence.
 

Trainfan344

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Is there more allowance for trains going downhill? For example a heavy freight train going down the Lickey incline going over the speed limit by 1 or 2mph before being brought under control?
 

ComUtoR

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That would be poor train control (at lest for us) Good practice is to have your speed under linespeed for the apex and then as the unit goes over and picks up speed you reduce any likelyhood of speeding. Allowing for the gradient is part and parcel of driving trains.
 
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