Signalling and 140mph running

[mp01]

Sorry if this is a dull question...

I've read several places that new(ish) 140mph trains can't run that fast because the signals aren't far enough apart, presumably for trains to stop safely. My question is why haven't train braking systems improved sufficiently over the years to mean that a newer train can be stopped in a shorter distance, and is hence allowed to travel faster?

As I said, might be a dull question, and I might be missing the point.

 

[tbtc]

FIrstly I think the speed is something to do with having sufficient time to see a signal (it must be visible to the driver for a few seconds?)...

...secondly it may be physically possible to brake from 140mph to nil in a few seconds, but I can't imagine it feeling very comfortable.

125 is fast enough for most lines as far as I'm concerned. Going faster creates problems exponentially.

 

[IanXC]

My understanding is that its based on the driver's ability to actually see the signal, someone more knowledgeable will say but there was some reseach done at about the same time as the "flashing yellow" trials on the ECML which said that 125mph was the maximum speed for the driver to reliably read the signal.

There was a need to alter the spacing of signals when HSTs were introduced to make sure there were sufficient stopping distances (although I read that the GWML didnt need these works as the GWR had used greater spacing initially).

After 125mph the only realistic signalling is in cab a la HS1.

 

[ainsworth74]

there was some reseach done at about the same time as the "flashing yellow" trials on the ECML which said that 125mph was the maximum speed for the driver to reliably read the signal.

It was a flashing green aspect, and in fact still does

But your right testing was done on the ECML in the Stoke Bank area (I think) where a flashing green aspect was added to some signals to authorise 140mph running. However the results of the trial were that it was felt that drivers couldn't be expected to reliably read the signal and react at those speeds hence for anything over 125 in this country you have to have in-cab signalling.

I would also expect as tbtc says it would probably also require increasing the distances between signals, which would be very complex (and expensive) on a route as complex and intensively used as the ECML.

I would also agree with tbtc when they say that 125 is plenty fast enough on the 'classic' lines, far better to spend time and money raising lines speeds on those lines that are currently sub 100mph than increasing those lines that are already at 125mph.

 

[jon0844]

But why did they go with 125mph? Because that is what it was? I mean, why couldn't they have said 130 or 135?

We know that some MK4s have been taken to 140mph there, but I do wonder if they did thorough testing or simply opted to do nothing as it was easier/cheaper.

 

[O L Leigh]

My question is why haven't train braking systems improved sufficiently over the years to mean that a newer train can be stopped in a shorter distance, and is hence allowed to travel faster?

Signal spacing defines the distance you have available in which to stop the train, but the braking characteristics of the train are only one part of the equation.

The physics of driving a train are very little different to those of driving a car. The limit of your braking and acceleration is defined by the limit of grip you have with the road. If you apply more brake force to the wheels than the grip levels permit you will break adhesion, lock the wheels and go into a slide that will serve to lengthen your braking distance. Therefore better brakes are not necessarily the answer, as you don't know that you won't hit a section of poor rail adhesion or something else that might affect your brake.

But the big problem is that, no matter how fast you are travelling, the amount of space you have to brake to a stop is fixed and defined by the signal spacing. Using the Highway Code's table of braking distances for road vehicles as a guideline, a vehicle travelling at 140mph requires almost 20% more distance to stop than a vehicle travelling at 125mph*. If the signal spacing along a given route allows you enough space to stop from 125mph within the three signal sections between the double yellow and red, you're going to need nearly four signal sections to stop from 140mph and the current system of fixed lineside signalling does not permit this. Attempting to do this under the current signalling regime is a recipe for disaster.

While an increase in linespeed from 125mph to 140mph may appear to be modest, the impact that it can have is immense.

O L Leigh

* The formula for calculating the stopping distance for road vehicles is:

x² ÷ 20 + x = Stopping distance in feet
x = vehicle speed in mph.

Go ahead and do the maths. It might just surprise you.

 

[Wyvern]

But why did they go with 125mph? Because that is what it was? I mean, why couldn't they have said 130 or 135?

Just to butt in. I think the 125 was an arbitrary figure set in the sixties. They'd achieved 100mph running, the next target was 125mph with the HST and the target after that would be 150mph with the APT.

POSTSCRIPT: The 225 in InterCity Project refers to Kph

 

[rail-britain]

I've read several places that new(ish) 140mph trains can't run that fast because the signals aren't far enough apart, presumably for trains to stop safely. My question is why haven't train braking systems improved sufficiently over the years to mean that a newer train can be stopped in a shorter distance, and is hence allowed to travel faster?

As always, you need to take into account older rolling stock and/or the slowest train, and what it is capable of
However, let's assume the track is clear for a train to proceed at 140mph
The main issue with the current signalling is not the distance between the signals (in a sequence from clear to danger), but the lack of sequencing and the subsequent distance

The first issue is driver reaction time, then train equipment reaction time
Fair enough the driver sees a signal at double yellow, however the time from seeing this to the brakes being fully applied is near on five seconds, and at the current 125mph that is nearly 1/8th of a mile (220 yards)
The final issue here is seeing such signals in extremely poor weather conditions (such as fog or snow)

When the InterCity 225 project was progressing for the implementation of the 140mph, it was clear an additional signalling sequence block would be required, hence the addition of flashing green
Although an InterCity 225 was capable of stopping from 140mph within the current signalling system, in wet conditions the train was right on the limit and in some tests it was shown it would pass the red signal (but it wasn't by much)

In the same way as most modern cars now operate by electronic systems, the HST for 125mph operation does the same
Hence why Mark 3 coaches can operate at 125mph, unlike the Mark 3a/b which cannot (as they are not fitted with the additional relays)

The final issue are the unions (why does it always come back to this!)
They are adamant that for train speeds of 140mph and above that an additional safety system must be installed, and the latest that Network Rail can offer is an in-cab signalling system
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I think the 125 was an arbitrary figure set in the sixties

Ironically, they were actually aiming for 120mph (in passenger use)
On the test runs between York and Darlington they showed the train could "easily" operate at 125mph, hence the record that was set in "normal passenger use"
Also, this was retained as the train brand name as it sounded better than InterCity 120
Ironically, many of the speed limits along the ECML were actually 120mph rather than 125mph, as many of the crossovers had been replaced around this 120mph upgrade work
With the later electrification many of those crossovers were upgraded again, taking many of them from 120mph to 140mph

 

[jopsuk]

Don't think anywhere in the world runs over 200km/h (125mph ish) without in cab signalling- I'm pretty sure there's few systems that run past 160km/h without some form of at least replication of line side signals to the cab- though the fundamental basis of many signalling systems is completely different to that used in the UK.

 

[Wyvern]

The final issue are the unions (why does it always come back to this!)

There was no need for that comment. The unions (if they are working properly) are the only protection people have, particularly in a privatised railway.

 

[The Planner]

Ironically, many of the speed limits along the ECML were actually 120mph rather than 125mph, as many of the crossovers had been replaced around this 120mph upgrade work
With the later electrification many of those crossovers were upgraded again, taking many of them from 120mph to 140mph

How many of the switches on the ECML are 125mph capable/rated though. I though it was only the ones on the Selby diversion that have it ?? Im sure this one has been discussed before somewhere.

 

[Peter Mugridge]

Hence why Mark 3 coaches can operate at 125mph, unlike the Mark 3a/b which cannot (as they are not fitted with the additional relays)

That's interesting because the data panels on the end of all the Virgin Trains Mk3s before the 390s took over read "max speed 125mph" even though they were only used at 110mph.

Has anyone checked the panels on the displaced examples and the sole remaining VT rake to see if any are still marked thus?

 

[shinkansen1966]

Don't think anywhere in the world runs over 200km/h (125mph ish) without in cab signalling- I'm pretty sure there's few systems that run past 160km/h without some form of at least replication of line side signals to the cab- though the fundamental basis of many signalling systems is completely different to that used in the UK.

What happens on the line between the end of the LGV near Tours and Bordeaux. There, do TGVs run at 137mph 220km/h on the classic line and with an additional signalling aspect. No sure, though...

 

[jopsuk]

What happens on the line between the end of the LGV near Tours and Bordeaux. There, do TGVs run at 137mph 220km/h on the classic line and with an additional signalling aspect. No sure, though...

The French use this

 

[rail-britain]

That's interesting because the data panels on the end of all the Virgin Trains Mk3s before the 390s took over read "max speed 125mph" even though they were only used at 110mph

All Mark 3a and Mark 3b coaches are marked "Max Speed 125mph"
However this is the design speed, not the operating speed
In order to operate at 125mph they would need to have the additional brake relays fitted

 

[Old Timer]

All Mark 3a and Mark 3b coaches are marked "Max Speed 125mph"
However this is the design speed, not the operating speed
In order to operate at 125mph they would need to have the additional brake relays fitted

The maximum speed stencilled on the vehicle end is the maximum speed that the vehicle may operate at.

Mk3s are conventionally air braked and do not have relays. Relays are only fitted to rolling stock that has electronically controlled braking systems.

The brakes are applied by a distributor on each vehicle, which reacts to pressure changes in the brake pipe, which is in effect a "control" pipe, as the air for the brakes is drawn from the main reservoir supply via the air reservoir tanks.

Mk3 stock had slightly modified brake pressures to allow the train to stop within the then existing braking curves, as opposed to the rest of the air-braked fleet.

 

[TDK]

As always, you need to take into account older rolling stock and/or the slowest train,

older rolling stock does not come into it as they will not be doing 140mph, only the TPWS would be an issue in this case

Ironically, they were actually aiming for 120mph (in passenger use)
On the test runs between York and Darlington they showed the train could "easily" operate at 125mph, hence the record that was set in "normal passenger use"
Also, this was retained as the train brand name as it sounded better than InterCity 120
Ironically, many of the speed limits along the ECML were actually 120mph

I find that bizarre that they opted on 125 opposed to 120 just because it sounds better, so would it be 135 instead of 140 if it is ever implimented?

I would say that the post above by O Leigh is more accurate.

 

[Old Timer]

older rolling stock does not come into it as they will not be doing 140mph, only the TPWS would be an issue in this case



I find that bizarre that they opted on 125 opposed to 120 just because it sounds better, so would it be 135 instead of 140 if it is ever implimented?

I would say that the post above by O Leigh is more accurate.

125 mph was always the target, although the HST protypes were tested to 130mph.

Stopping from 130 mph could not be achieved whilst stopping from 125 mph COULD be achieved within the existing signalling, that is why the HST is restricted (in part) to 125 mph.

 

[rail-britain]

Mk3s are conventionally air braked and do not have relays. Relays are only fitted to rolling stock that has electronically controlled braking systems

Compare the brake systems of the Mark 3 (HST) to the Mark 3a/b then
Yes, the braking components are the same, that a Mark 3a coach cannot be used behind a HST power car at more than 110mph
If you want confirmation of this contact Porterbrook
I worked on HSTs out of Aberdeen and Edinburgh in the late 1990s, so am aware of all the subtle differences between then

 

[Old Timer]

I worked on HSTs out of Aberdeen and Edinburgh in the late 1990s, so am aware of all the subtle differences between then

And I was involved in the introduction of them to the Eastern Region in 1978.

HST MK3 vehicles do not have buffers and are wired to take the the HST control circuits In addition the HST stock has duplicated brake and MRP pipes on each side of the train. I will leave you to ponder why this is so.

As far as electrical wiring is concerned, the loco hauled Mk3 vehicles take a standard single phase 1000 V AC or DC train heat supply from the locomotive and convert it through motor alternator units located under the floor. These convert the train supply to 3-phase 415/240 V 50Hz AC to power air conditioning and other ancillaries.

The Mk3b stock had/has an improved MA unit and a different seating arrangement

The HST stock in contrast takes a 440 voltage/frequency 3-phase supply directly from an auxiliary alternator in the power car to supply on board equipment such as the air conditioning, PA and other electrical services. This difference makes the two types non-interconnectable in service conditions.

Restrictions to 110mph on Mk 3 stock relates to the maximum speed of the hauling locomotive. Only the Class 87s and 90s were authorised to run at 110 mph.

 

[captainbigun]

Restrictions to 110mph on Mk 3 stock relates to the maximum speed of the hauling locomotive. Only the Class 87s and 90s were authorised to run at 110 mph.

Ahem, and the 86/1s and a selection of 86/2s.

A conventional hauled Mk3 can be hauled at 125 subject to there being a DVT at the other end and the hauling loco, 89 or 91 being at the other. It is a equirement for 125mph running in such a configuration that the brake pipe is controlled at both ends of the train (i.e. via the TDM).

 

[Old Timer]

Ahem, and the 86/1s and a selection of 86/2s.

Three 86s (which were renumbered in the series 86/1) were modified with new bogies and transformers of a design developed for use in the Class 87s, then under development. These were the only Class 86 variants authorised to run above 100, being limited to 110

When you speak of 125 mph I presume you are referring to E3173 which reached 129 mph in the Cheddington area whilst undergoing trials in the mid-1970s ?

It is a equirement for 125mph running in such a configuration that the brake pipe is controlled at both ends of the train (i.e. via the TDM).

The DVT is simply that. The brake control comes from the locomotive not the DVT.

I presume you are getting confused with train wire 13 and its equvalent ?

 

[captainbigun]

Three 86s (which were renumbered in the series 86/1) were modified with new bogies and transformers of a design developed for use in the Class 87s, then under development. These were the only Class 86 variants authorised to run above 100, being limited to 110

When you speak of 125 mph I presume you are referring to E3173 which reached 129 mph in the Cheddington area whilst undergoing trials in the mid-1970s ?

86/1s have BP9s but don't and never did carry 87 transformers. Urban myth that one. There weren't enough 87 transformers to go around to allow that. There were only two float. Several 87s ended up with 86 transformers. Several 86/2s (86209, 86211, 86224, 86225, 86231 and several others which swapped in and out of the fleet) were authorised for 110mph to supplement the 87s required for the 110mph operation in the 80s.

86701 and 86702 are also authorised for 110mph.
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[/SIZE] The DVT is simply that. The brake control comes from the locomotive not the DVT.

Not so, brake pipe control via TDM on 89/90/91, three channels allocated to this. 8 steps of brake available which corresponds to the E70/DW3 control. This allows quicker control of the brake pipe.

 

[Old Timer]

86/1s have BP9s but don't and never did carry 87 transformers.

I suggest you read what I wrote.

 

[captainbigun]

I suggest you read what I wrote.

I did....I don't think I've misread it. 86/1s do have BP9s but they've never carried anything other than a conventional 86 transformer. They also have 87 (SH152) chokes.

I'm intimately familiar with 86s and 87s....

 

[Old Timer]

Not so, brake pipe control via TDM on 89/90/91, three channels allocated to this. 8 steps of brake available which corresponds to the E70/DW3 control. This allows quicker control of the brake pipe.

Demonstrating a lack of understanding of the brake system.

To help you I will point out that the brake controller in the DVT transmits the brake control instructions to the LOCOMOTIVE which then applies the brake. The 86s used on DVT working did not have 8 step controls.

Reference to Class 89/91 and brake controls are only relevant when comparing them to the Class 90.

In any case the discussion is about Mk3 and loco-hauling and not about Class 89/91
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I'm intimately familiar with 86s and 87s....

Then I suspect you should put the AC Electric Locomotive Group right ?

My words stated that the transformer was the one being developed for the Class 87. THis fact was announced in the Railway technical press and modern Railways at the time. I presume they are wrong too ?

 

[captainbigun]

Demonstrating a lack of understanding of the brake system.

To help you I will point out that the brake controller in the DVT transmits the brake control instructions to the LOCOMOTIVE which then applies the brake. The 86s used on DVT working did not have 8 step controls.

Reference to Class 89/91 and brake controls are only relevant when comparing them to the Class 90.

In any case the discussion is about Mk3 and loco-hauling and not about Class 89/91

No, not correct. The DVTs also have a brake application unit. This is isolated when used with an 86 or 87, but is operational when used with a 89/90/91. I can share the drawings with you if it helps!
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Then I suspect you should put the AC Electric Locomotive Group right ?

AC Loco Group....yes, that's one of many details not entirely correct. The transformers are interchangeable between 86 and 87 so it's not impossible.
--- old post above --- --- new post below ---

My words stated that the transformer was the one being developed for the Class 87. THis fact was announced in the Railway technical press and modern Railways at the time. I presume they are wrong too ?

Yes, it would appear so. There was no real need to test the transformer, only small differences, uprated secondary and tertiary windings, and a slightly improved selector tank.

 

[Old Timer]

This is isolated when used with an 86 or 87, but is operational when used with a 89/90/91. I can share the drawings with you if it helps!

No that will do for me. You have proven your worth

Anyway re the transformers I am aware they are interchangeable but if you check you will find that the original transformers used on the 86/1 was of the type being developed for the 87s. I do not recall the reason or the history beyond that - old age means some things like this get forgotten over time

 

[captainbigun]

OT, nothing personal by the way. I've spent a lot of hours over the past couple of years rummaging around 86s (86101, 86213 etc etc) and 87s (most of them) as well as the 89 and a handful of DVTs. A selection of subjects I've come to gain a lot of knowledge in, not least from a variety of WB, WN and LNWR residents as well as piles of paperwork.

 

[Old Timer]

OT, nothing personal by the way. I've spent a lot of hours over the past couple of years rummaging around 86s (86101, 86213 etc etc) and 87s (most of them) as well as the 89 and a handful of DVTs. A selection of subjects I've come to gain a lot of knowledge in, not least from a variety of WB, WN and LNWR residents as well as piles of paperwork.

Absolutely no offence taken old chap.

Next time you find an 86 going for cutting save something for me, eh ? Please ?