A question about speed limits

[eldomtom2]

This has been a question I've been wondering about for a while now. Is there a specific point where a train is deemed to have exceeded the speed limit, and if so, what is it? If the speed limit is, say, 60mph, at what speed would a train be considered to be exceeding it? 60.0mph? 60.1mph? 61.0mph? Is it even thought about to that level of detail?

 

[Snow1964]

It is certainly not down to tenths of a mph

With analogue (dial) speedometers not going to be that accurate within 2mph, and will be slight reading error depending on alignment of needle from eyes.

Then there is calibration, unless they have been very accurately set up when the wheels last turned (on whichever axle drives the speedometer) likely to misread couple of percent.

But technically 61mph in 60mph zone is exceeding the limit.

However various accident reports over the last 50 years seem to suggest derailments have been when trains are something like 80%+ over the limit, so there is often a huge safe margin built in.

 

[12LDA28C]

This has been a question I've been wondering about for a while now. Is there a specific point where a train is deemed to have exceeded the speed limit, and if so, what is it? If the speed limit is, say, 60mph, at what speed would a train be considered to be exceeding it? 60.0mph? 60.1mph? 61.0mph? Is it even thought about to that level of detail?

I'd like to see you measure 60.1mph on an analogue speedometer on a train. If I was reading an OTMR download for example, I would not consider 60.1mph or even 61mph to be 'speeding'. If however speed was increasing to the realms of 64/65mph then I would say the driver was speeding.

Personally I would allow for a discrepancy of around 10% at lower speeds (say 16.5mph in a 15mph limit) and a diminishing percentage the higher the line speed.

 

[Horizon22]

My understanding is that +/-3mph is often used however that seems to be to be more “unfair” at higher speeds so there may be more to it than that.

 

[12LDA28C]

My understanding is that +/-3mph is often used however that seems to be to be more “unfair” at higher speeds so there may be more to it than that.

Not as simple as that. If a driver were found to have been travelling at 8mph in a 5mph siding, that would almost certainly be classed as 'speeding'. A driver travelling at 103mph within a 100mph limit - probably not.

I suggest different FOCs / TOCs have their own guidelines and even those may be interpreted / applied differently by different departments / individuals.

 

[Ken H]

How many speed limits are to stop derailments and how many to limit cant deficiency for the passengers. The west coast on BR increased speed limits by allowing a greater lateral acceleration for passengers. Together with 110mph running this gave a useful journey time cut between London and Glasgow.

 

[Llanigraham]

I was told on the Cambrian that the system allowed 10% over the signed limit.

 

[ComUtoR]

If I was reading an OTMR download for example, I would not consider 60.1mph or even 61mph to be 'speeding'.

How many downloads have you read ?

I would be looking for other factors rather than just the technical speed the Driver was doing. 60.1mph would be over and you would certainly need to note it.

Personally I would allow for a discrepancy of around 10% at lower speeds (say 16.5mph in a 15mph limit) and a diminishing percentage the higher the line speed.

I'm interested to why you would allow different percentages for different speeds.

I suggest different FOCs / TOCs have their own guidelines and even those may be interpreted / applied differently by different departments / individuals.

My TOC has a strict limit on when action should be taken against a Driver for 'speeding' it's all laid down in our company standards. I would absolutely say that the limit set forms part of their safety case.

 

[AM9]

My understanding is that +/-3mph is often used however that seems to be to be more “unfair” at higher speeds so there may be more to it than that.

Although at high speeds (for the route), the train is more likely to be running at a constant speed, whereas in areas where there is a low speed PSR because of a historic alignment shortfall, the essential part of speed adjustment should be completed well before the critical point. How does historical data of speed limit violations compare with those different types of speed limit.

 

[12LDA28C]

How many downloads have you read ?

Many.

== Doublepost prevention - post automatically merged: 18 Dec 2022 ==

I would be looking for other factors rather than just the technical speed the Driver was doing. 60.1mph would be over and you would certainly need to note it.

Absolutely not. A driver would not be able to differentiate between 60mph and 60.1mph on an analogue speedometer, and anyway the driver should be concentrating on the road ahead, not staring at the speedometer.

== Doublepost prevention - post automatically merged: 18 Dec 2022 ==

I'm interested to why you would allow different percentages for different speeds.

Again, because of the characteristics of an analogue speedometer and the angle at which a driver views it, not to mention any associated inaccuracy / calibration discrepancies.

10% above line speed at say 11mph in a 10mph limit is of little concern however 137.5mph in a 125mph limit is rather more worrying, wouldn't you say?

 

[Cherry_Picker]

ATP gives a warning at speed limit +3mph and intervenes at speed limit +5mph. I doubt there’s a national standard which matches what ATP does but it’s a point of reference.

It’s also worth pointing out that there are often multiple speedometers on a train and while they should be calibrated to match, the speed the driver sees on the desk might be different to what shows up on the OTMR.

Pulling someone in for 0.1mph over the limit would be laughable and that manager would really need to pick their battles.

 

[ComUtoR]

Absolutely not. A driver would not be able to differentiate between 60mmph and 60.1mph on an analogue speedometer, any anyway the driver should be concentrating on the road ahead, not staring at the speedometer.

As mentioned, I would be looking at other factors too.

One of which is if the Driver was braking. I would also note it for future reference. If a Driver was consistently over the speed limit I would be having a word in their shell like. If the unit consistently read as over then I would flag it to engineering. If the download was part of a TPWS trip then is be gutted but still following company procedures.

 

[12LDA28C]

It’s also worth pointing out that there are often multiple speedometers on a train and while they should be calibrated to match, the speed the driver sees on the desk might be different to what shows up on the OTMR.

Indeed. The only way to be sure would be to be in the cab with the driver and then download the train as well.

== Doublepost prevention - post automatically merged: 18 Dec 2022 ==

Pulling someone in for 0.1mph over the limit would be laughable

Absolutely. It just wouldn't happen.

 

[ComUtoR]

10% above line speed at say 11mph in a 10mph limit is of little concern however 137.5mph in a 125mph limit is rather more worrying, wouldn't you say?

Our limits are set by the company standards. Those are the only limits I can go by because it ensures that everyone is treated equally and there is no room for "interpretation" or any personal justifications either way.

Drivers are pretty good at following the speed limits. We tend to be on the more cautious side, rather than being slightly over all the time.

 

[Master29]

So in laymans terms yes but very minor infringements at any speed but best not to make a habit of it.

 

[12LDA28C]

Our limits are set by the company standards. Those are the only limits I can go by because it ensures that everyone is treated equally and there is no room for "interpretation" or any personal justifications either way.

Drivers are pretty good at following the speed limits. We tend to be on the more cautious side, rather than being slightly over all the time.

Not too sure where I said that drivers are 'slightly over all the time'.

To clarify, I'm saying that if a driver were to exceed the line speed at a certain point, factors would be taken into consideration such as by how much the limit was exceeded and for how long, was any remedial action taken (brake application) etc.

Maybe some TOCs have figures set in stone for these kinds of events, if so I'm not sure that's particularly useful.

 

[whoosh]

Even a digital speedometer only differentiates in full, whole, miles an hour.

That's right folks, only the railway could have "standards" written in a cosy office with the luxury of decimal point accuracy downloads used to assess, but the people out in the field are given analogue instruments or digital ones that round to nearest mph.

This is the sort of thing that breeds eye rolling between the coal face and management.

 

[ComUtoR]

Not too sure where I said that drivers are 'slightly over all the time'.

That wasn't aimed at anyone, just a statement.

To clarify, I'm saying that if a driver were to exceed the line speed at a certain point, factors would be taken into consideration such as by how much the limit was exceeded and for how long, was any remedial action taken (brake application) etc.

Which is what I initially stated. Downloads are so much more than just 'data'. Especially when downloads aren't all equal and some are pretty much garbage.

Maybe some TOCs have figures set in stone for these kinds of events, if so I'm not sure that's particularly useful.

I would say mainly because there should be a standard in place as part of the (CMS) competency management system, and that it stops one person getting away with it because their mate read the download and one getting crucified because of tiny error. I would also say it would be because (as mentioned upthread) there are inaccuracies with both the data and the actual speed of the unit. One unit I used to drive had
speedos in the cab that could all read different. If someone was doing 4mph through the wash and caused damage then should they get pulled for speeding ? Yet someone who trips the grids by 0.1mph gets that incident on their record. Having set values and set procedures removes those grey areas.

From the group standards :

2.6.2 Speed indicating equipment test report
2.6.2.1 The speed indicating equipment test report shall record: a) The indicated speed readings against the set test speeds; b) Whether the accuracy of the readings meet either: i) The required accuracy of ± 2 mile/h (± 3 km/h) over the whole speed range, when compared with calibrated test equipment, during a static test; OR ii) The requirements of the appropriate standards set out by the railway undertaking where this accuracy is different from ± 2 mile/h (± 3 km/h). c) Whether any fault conditions were found or suspected.

https://www.rssb.co.uk/standards-catalogue/CatalogueItem/RIS-2273-RST-Iss-2 (account login required)

 

[12LDA28C]

I would say mainly because there should be a standard in place as part of the (CMS) competency management system, and that it stops one person getting away with it because their mate read the download and one getting crucified because of tiny error.

If that's the standard of your driver assessors then that seems to highlight a different issue and one that should certainly be addressed. I'm sure no matter whatever standard is in place that an assessor could ignore/overlook certain transgressions if they wanted to 'let a mate off', so it rather depends on the integrity of those doing the assessing as to whether or not the standards are correctly applied.

 

[66701GBRF]

How many downloads have you read ?

I would be looking for other factors rather than just the technical speed the Driver was doing. 60.1mph would be over and you would certainly need to note it.




I'm interested to why you would allow different percentages for different speeds.



My TOC has a strict limit on when action should be taken against a Driver for 'speeding' it's all laid down in our company standards. I would absolutely say that the limit set forms part of their safety case.

.1 over needs to be noted? You are having some kind of laugh. I'd be interested to hear how many downloads you have read and have had to act on.

 

[Efini92]

My understanding is that +/-3mph is often used however that seems to be to be more “unfair” at higher speeds so there may be more to it than that.

The old Northern Rail SMSP said anything upto 3mph was to be disregarded.
Over 10mph and the driver was to be Med Screened and suspended pending investigation.

 

[Purple Train]

I seem to remember reading an RAIB report into an over-speed at Fletton Junction where the speed limit was 25mph on points designed for a maximum speed of 27mph. Are speed limits usually that close to the maximum "safe" speed, or do they allow a more generous margin of error in case of minor over-speeds?

 

[Kneedown]

When I did a spot of Driver Managing we used to give a leeway of + 3mph to allow for speedo discrepancy. Anything more i'd look to see if it was just a brief overspeed quickly corrected, or if excess speed was sustained for a longer period. If just a brief overspeed we'd note it on the download and feed it back to the Driver but no action would be taken. Anything sustained though, and action would be dependant on how high the excess was, for how long, and location. Anything from a suitable conversation, up to disciplinary action.

 

[Annetts key]

Speed limits may be present for reasons other than the actual capability of the track. Some examples: insufficient signal spacing for a faster speed, substandard service breaking distance between a signal displaying a restrictive aspect and a more restrictive aspect, hence needing a permanent speed restriction, on the approach of a level crossing (including over a level crossing) or due to limitations with the available structure gauge.

A slight increase of speed over the speed limit is unlikely to significantly increase the likelihood of a derailment in most cases. However, it may cause more wear of the rail(s).

Obviously a significantly higher speed above the limit is a safety issue.

Railtrack/Network Rail have occasionally been known to use portable speed measuring equipment (radar guns I think) to check the speeds of trains in areas of concern.

 

[craigybagel]

Even a digital speedometer only differentiates in full, whole, miles an hour.

As always with the railway there's an exception to the rule, that being the Class 67 which shows .1 decimal increments below 10mph on its digital speedo. It has always seemed a little odd to me that strictly speaking on the depot I'm limited to 5.0 mph, whereas with everything else I drive (including the DVT usually attached to said 67) I could go all the way to 5.9 and not knowingly be speeding, but I guess at those low speeds it doesn't make much difference - and it's not like it's easy to hold a 67 at exactly 5.0 anyway.

 

[king_walnut]

I've heard that if you're caught doing 5mph over the speed limit then you have to be referred to a Network Rail panel who investigate it and decide if you can keep your key? Is that a thing or just scare tactics?

 

[D365]

It’s also worth pointing out that there are often multiple speedometers on a train and while they should be calibrated to match, the speed the driver sees on the desk might be different to what shows up on the OTMR.

It doesn't help that, within some fleets, vehicles are fitted with differing speedos and speedo drives. Sometimes on a painted number basis!

 

[class68fan]

When it was done with a man pointing a speed gun at a train there were a scale. 0-somerthing = no action/somerthing - somerthing = quiet word/ over that = Form 1.

 

[Railsigns]

I seem to remember reading an RAIB report into an over-speed at Fletton Junction where the speed limit was 25mph on points designed for a maximum speed of 27mph. Are speed limits usually that close to the maximum "safe" speed, or do they allow a more generous margin of error in case of minor over-speeds?

The safety margin for overspeeding is included in the design speed of the points. For example, if a track design states that a set of points is designed for 40 mph, then it's safe to set the permissible speed at 40 mph.

 

[brad465]

While not the real world, on Train Simulator you get penalised/flagged for going 1mph+ over the speed limit, regardless of what the speed limit is.