Speed limits and making up time

[Monty]

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?

There is no allowance under any circumstances, it's called a speed limit for a reason. It's up to the driver to ensure his train is properly under control at all times regardless of the ruling gradient or speed limit.

 

[driver9000]

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.

That's the 50 through Chorley station but it isn't used any more since OTDR covers it function.

Coppull hot axle box detector has a Speedchex device which flashes up the speed on a screen in the power box.

 

[Trog]

For example, was this when (and why) the Hele/Cullompton curves north of Exeter went up?

Cullompton is a special case and has 8" of cant instead of the normal maximum of 6", so as to avoid having a speed restriction in the middle of an other wise fast run..

 

[Kentish Paul]

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.

Never knew that. Many a trip from Bristol to Cardiff sat behind the driver the speedometer needle sat squarely on the 70mph mark.

 

[Senex]

Cullompton is a special case and has 8" of cant instead of the normal maximum of 6", so as to avoid having a speed restriction in the middle of an other wise fast run..

Thanks for that -- I didn't know so much cant had been used anywhere in this country.

 

[edwin_m]

I've always wondered if the increase in cant deficiency is the reason the Mk3 saloon sliding doors don't stay closed. Can anyone confirm or correct me?

 

[Phil.]

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.

Well that's news to me. I've worked on "classic" DMUs from Cravens, Metro-Cammell, BRC&W, B.R. Derby et al and I've never encountered an overspeed device There was an engine overspeed trip but that was to prevent engine damage, not to prevent the train from exceeding it's 70 mph limit.

 

[Wookiee]

REPs over the ton down the hill to Winchester

I was walking through an 8xTC hauled by a pair of 73s as it exited the Popham tunnels and the speedo in one of the middle cabs said 109mph. I've no idea how reliable it would have been, particularly as it was the rear-facing cab, but it certainly seemed to be going at a fair old rate!

 

[Deepgreen]

I recall an occasion in December 1981, when a major snowfall hit southern England, and the then Victoria to Bognor Regis evening peak working via Sutton and Dorking was instructed to call additionally at Epsom, owing to a lack of local trains running. We were late anyway when I boarded at Sutton (onto the buffet car) and we hurtled away up to at least 85mph, with the line speed being 60! Quite surreal, being in an operating buffet car on a suburban journey through heavy snow!
--- old post above --- --- new post below ---

I was walking through an 8xTC hauled by a pair of 73s as it exited the Popham tunnels and the speedo in one of the middle cabs said 109mph. I've no idea how reliable it would have been, particularly as it was the rear-facing cab, but it certainly seemed to be going at a fair old rate!

Shouldn't make any difference whether front- or rear-facing.

 

[QueensCurve]

Well that's news to me. I've worked on "classic" DMUs from Cravens, Metro-Cammell, BRC&W, B.R. Derby et al and I've never encountered an overspeed device There was an engine overspeed trip but that was to prevent engine damage, not to prevent the train from exceeding it's 70 mph limit.

I was told this many years ago by an internal source I considered reliable but who would have no direct experience of driving the sets.

As such, I had no reason to doubt that the engine speed governor would limit the sets to 68mph.

If anyone can add to this I would be grateful for the information.

 

[Kentish Paul]

I was told this many years ago by an internal source I considered reliable but who would have no direct experience of driving the sets.

As such, I had no reason to doubt that the engine speed governor would limit the sets to 68mph.

If anyone can add to this I would be grateful for the information.

I have no reason to doubt you but to add to my post above when travelling along the flat between Severn Tunnel Junction and Newport at 70mph and a bit over the controller was left at maximum and the engines never cut out.
I find it hard to believe that a late 1950s DMU would have the technology to cut engine power at 68mph.

 

[QueensCurve]

I have no reason to doubt you but to add to my post above when travelling along the flat between Severn Tunnel Junction and Newport at 70mph and a bit over the controller was left at maximum and the engines never cut out.
I find it hard to believe that a late 1950s DMU would have the technology to cut engine power at 68mph.

I am intrigued now. Quite apart from doubting my source, I am wondering if there is something other than a DMU that had this property.

I will say that that any governor on the engine would have been quite crude not limiting the speed as such but simply cutting the power until speed had fallen well below again.

 

[LNW-GW Joint]

Track speed limits must be generally over-cautious though, in the interests of simplicity and "drivability".
Specific limits will be there for certain structures and conditions (signal sighting etc), but much of the plain line, straight route will probably be good for a faster speed but not signed as such.
Then there's the maintenance regime, which is tied to costs.
You could probably have a higher speed on some sections, but the access charges would be higher, because of the increased wear and tear on the track.

One of the conundrums on the WCML is why none of it is signed for 125mph for non-tilt trains, even where it is as straight as the ECML/GWML.
Today it doesn't matter as all the main services tilt, but as soon as TOCs want to run 125mph-capable AT300s or LHCS over it (or HS2 non-tilt classic compatibles), there will need to be a re-evaluation of the route speeds.
Or am I talking rubbish?

 

[MichaelAMW]

I have no reason to doubt you but to add to my post above when travelling along the flat between Severn Tunnel Junction and Newport at 70mph and a bit over the controller was left at maximum and the engines never cut out.
I find it hard to believe that a late 1950s DMU would have the technology to cut engine power at 68mph.

I also doubt this 68mph idea for two reasons:

-- Similar experiences in 115 DMUs exceeding 70mph with no let up in the engines
-- The simple fact that most of the 1st-generation DMUs had a stated maximum speed of 70mph so it seems surprising that they would be limited to something less than that

 

[Kentish Paul]

I am intrigued now. Quite apart from doubting my source, I am wondering if there is something other than a DMU that had this property.

I will say that that any governor on the engine would have been quite crude not limiting the speed as such but simply cutting the power until speed had fallen well below again.

Back in the day you are refering to there was no automatic speed control. If a class 47 driver (95mph max) wanted to do 115mph there was nothing to stop him. When HSTs came in 1976 I clocked them well above 125mph between Didcot and Reading (137mph). Speed limiters set to 128mph came later.
There is no way a classic DMU had any sort of speed limiter installed.

 

[neilb62]

Well that's news to me. I've worked on "classic" DMUs from Cravens, Metro-Cammell, BRC&W, B.R. Derby et al and I've never encountered an overspeed device There was an engine overspeed trip but that was to prevent engine damage, not to prevent the train from exceeding it's 70 mph limit.

Ditto, mind you our 117's would hardly get to 68 with a tail-wind...

 

[Carlisle]

I've always wondered if the increase in cant deficiency is the reason the Mk3 saloon sliding doors don't stay closed. Can anyone confirm or correct me?

The much more modern Pendilino saloon doors still don't always stay closed at speed either, so maybe it's more of a fundamental design issue

 

[Flying_Turtle]

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?

You don't overspeed heavy trains downhill....

 

[QueensCurve]

Back in the day you are refering to there was no automatic speed control. If a class 47 driver (95mph max) wanted to do 115mph there was nothing to stop him. When HSTs came in 1976 I clocked them well above 125mph between Didcot and Reading (137mph). Speed limiters set to 128mph came later.
There is no way a classic DMU had any sort of speed limiter installed.

Not a speed limiter, but an engine governor (a sort of balls to the walls thing) which would, by coincidence, have operated at a particular speed.

I am genuinely in doubt about the speed of this, and would still welcome more information.

 

[edwin_m]

First generation DMUs had a mechanical transmission with a multi-speed gearbox, so in a particular gear the relationship between engine speed and train speed is fixed (give or take a bit for wheel diameter and other tolerances). If there was some sort of engine governor it would have had the effect of putting a fixed speed on achievable speed in top gear, although probably allowing overspeed on a steep enough downward gradient. This is unlike electric transmissions where an engine governor would limit power, and the achievable speed would then depend on gradient and other things.

There's lots of technical info on railcar.co.uk.

 

[Deepgreen]

You don't overspeed heavy trains downhill....

No, you shouldn't, but that wasn't what was asked. Downhill over-speeding is probably the most insidious and most dangerous, thus requiring most control to be exercised.

 

[ComUtoR]

Downhill over-speeding is probably the most insidious and most dangerous,

If that was the case then why aren't there more over-speed sensors on gradients ?

thus requiring most control to be exercised.

Not sure in all honesty. I find that using the technique I mentioned earlier I barely need to control my units. I simply make an allowance for the gradient and coast. We have one on a 90 mph downhill gradient where I'm in full power on the down and still barely need to think about the gradient. There is a 60mph PSR and a 40mph crossover to consider when running ECS etc but I can still power down through the gradient.

My main speeding concerns are TSR/ESR (temp/emergency speeds) or places where you get dramatic changes of speed. ie. a 70psr onto a 15psr (which is protected by TPWS/AWS)

 

[Deepgreen]

If that was the case then why aren't there more over-speed sensors on gradients ?

I don't know whether there are or not, but I imagine that there are as many, on average, as elsewhere, which should do the job just as well as on level track. It would be interesting to know though, what, for example, is provided at Lickey, to prevent uncontrolled/overspeed descents. Maybe nothing special is installed at such sites.

 

[edwin_m]

Signal spacings are increased on down grades and reduced on up grades to allow for changes in braking distances, but are still based on the permitted speed with no extra allowance for trains going out of control. As stated it is up to the driver to manage the train within the permitted speed, but provided they do so and brake promptly at adverse signals they should have enough track to stop short of a red.

 

[headshot119]

First generation DMUs had a mechanical transmission with a multi-speed gearbox, so in a particular gear the relationship between engine speed and train speed is fixed (give or take a bit for wheel diameter and other tolerances). If there was some sort of engine governor it would have had the effect of putting a fixed speed on achievable speed in top gear, although probably allowing overspeed on a steep enough downward gradient. This is unlike electric transmissions where an engine governor would limit power, and the achievable speed would then depend on gradient and other things.

There's lots of technical info on railcar.co.uk.

Not all first gen units had mechanical transmission.

And none I've ever worked on have a speed limiter.

 

[ComUtoR]

I don't know whether there are or not, but I imagine that there are as many, on average, as elsewhere, which should do the job just as well as on level track.

I'm searching my routes but I cannot think of any locations on my part of the network where there is an overspeed TPWS for a gradient. I'm sure in the rulebook it states where TPWS is placed. I'm not 100% without checking but I don't believe "gradients" are on of them.

They may be on a gradient somewhere on the network and I'd be interested to know where and why too.

 

[Huntergreed]

How difficult is it to keep a train on time? If you drive at the perfect speed limit, would you arrive on time or early? Is there grace time built in to timetables? Is slight speeding permitted during late running?

 

[trainmania100]

I think speeding will cause the emergency brake to apply, when going over an over speed loop on the track?
I imagine its hard keeping to schedule if your delayed for any reason. There must be some slack in the timetable in some places

 

[yorkie]

1. No straight answer to this as you've not given any parameters, so I don't think any drivers can answer the question as worded other than to say the answer will vary depending on the service and conditions.

2. Depends on the timetable.

3. Depends on the timetable (if you can think of some particular examples this could potentially be a thread in its own right in the timetabling forum)

4. On the railways it is actually a speed limit, so no.

 

[380101]

How difficult is it to keep a train on time? If you drive at the perfect speed limit, would you arrive on time or early? Is there grace time built in to timetables? Is slight speeding permitted during late running?

No speeding allowed to make up time.

Timetables can vary. some have time built in to account for slight delays; others don't.

Most drivers aim to keep to time but safety comes first always. DOO drivers face enormous pressure from having to ensure passenger safety at platforms and trying to keep on time. I personally as a DOO driver don't worry about being late - EVER! I aim to ensure my passengers arrive at their destination safely.

Sadly, most managers and politicians can't see past headline journey times which results in drivers and guards being stuck in the middle. Every driver and guard I work with always puts passenger safety before keeping on time.