Dangers of High Speed Trains Pushed from the Rear
 

1/ the rear power car, still under full power, caused much of the
crumpling and jack knifing, and

This is believed to be incorrect, but is in the interim HSE report
which might explain why it got posted here.

The unfounded idea that the rear power car was still under full power
was certainly NOT in the interim HSE report. It was an ignorant rumour
that I believe was mentioned first on Sky News a few hours after the
crash.
--

I can see where this has come about. There is a BBC website report that
states "The front of the First Great Western train ploughed into the
embankment, while the rear power car on the train continued to propel the
train forward, investigators found."

What they have missed out is "momentum of", which is in the HSE report.

...and the investigators might have pointed out that the momentum of the
rear eight coaches acting on the (derailed) leading power car was a lot
greater than the momentum of the rear power car.

David

I'm going to wander off topic here slightly... but i hope it's still
relevant.

Wasn't the Lockington accident made worse by the fact that a heavier
DMU set was at the rear?

If i recall correctly wasn't it a 105/114 pairing? Making it even
worse the 105 trailer car was leading (thus the lightest carriage of
the four), and class 105s being of shorter body length and pretty
appalling crashworthiness wise, would have made things worse. Shorter
bodylength being worse cos damage from front and behind on the first
carriage would be more catastrophic.

The 105 trailer struck the van on the level crossing and then the
heavier carriages behind kept it going and lots of track was damaged
leading to serious damage to all four vehicles.

So maybe there is a point about the heavier vehicles behind keeping
the train moving.

Slamdoor Mat.

Dangers of High Speed Trains Pushed from the Rear
 

On Thu, 11 Nov 2004 13:31:57 GMT someone who may be James Robinson
wrote this:-

- There is no mention of the power setting in the interim report.

Irrelevant. We know that with the brakes applied traction power
cannot be obtained.

It is possible that the control system was deranged during the
initial impact. However in that case the rear data recorder and the
front data recorder would disagree. I imagine this would be
mentioned by the RI.



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Dangers of High Speed Trains Pushed from the Rear
 

"Clive Coleman" wrote in message
...
In message , dwb
writes
econdly, the rear power car was NOT under the full power.
The train's 'black box recorder' that the power notch was at zero and
the brake handle was in 'emergency'. It was simply the inertia of the
rear power car (which had already derailed) that kept it moving.
Do you KNOW that?

Yes. To quote Network Rail's report:

"1C92 struck the car at 18:05/32. OTMR indicates that 1C92's brakes were
applied two to three seconds before the collision. Leading wheelset of 1C92
derailed on the crossing on impact with the stationary car."

--
*** http://www.railwayscene.co.uk/ ***
Rich Mackin (rich-at-richmackin-co-uk)
MSN: richmackin-at-hotmail-dot-com

Dangers of High Speed Trains Pushed from the Rear
 

Irrelevant. We know that with the brakes applied traction power
cannot be obtained.

Does this mean that any brake application automatically cuts traction power?

It's typical in North America to "power brake". In power braking, the
throttle is left in notch two or three, the independent brake in full
release while the train is brought to a stand with the train brake working
against the throttle. Is this not possible in the UK?


--
Cheers
Roger T.

Home of the Great Eastern Railway
http://www.highspeedplus.com/~rogertra/

Dangers of High Speed Trains Pushed from the Rear
 

On Thu, 11 Nov 2004 12:04:55 -0800, Roger T. wrote:



Irrelevant. We know that with the brakes applied traction power
cannot be obtained.

Does this mean that any brake application automatically cuts traction power?

It's typical in North America to "power brake". In power braking, the
throttle is left in notch two or three, the independent brake in full
release while the train is brought to a stand with the train brake working
against the throttle. Is this not possible in the UK?

You are also comparing a technique to handle slack in a long rake of
goods wagons with the operation of relatively short rake of passenger
rolling stock with low slack couplers and a locomotive on each end, not
just the front.

I would be surprised if goods trains in the UK didn't also use the 'power
brake' technique to stop the slack from running in.

Dangers of High Speed Trains Pushed from the Rear
 

On Thu, 11 Nov 2004 12:04:55 -0800 someone who may be "Roger T."
wrote this:-

Does this mean that any brake application automatically cuts traction power?

That is my understanding and it has been stated by others who are in
a position to know. Such an interlock appears to have been common
since the 1960s.


--
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I will always explain revoked keys, unless the UK government
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Dangers of High Speed Trains Pushed from the Rear
 

"Roger T." wrote
It's typical in North America to "power brake". In power
braking, the
throttle is left in notch two or three, the independent brake
in full
release while the train is brought to a stand with the train
brake working
against the throttle. Is this not possible in the UK?

Not with the stuff I drive. Why would you do that?
Nev

Dangers of High Speed Trains Pushed from the Rear
 

"Matthew Geier"

Irrelevant. We know that with the brakes applied traction power
cannot be obtained.

Does this mean that any brake application automatically cuts traction
power?

It's typical in North America to "power brake". In power braking, the
throttle is left in notch two or three, the independent brake in full
release while the train is brought to a stand with the train brake
working
against the throttle. Is this not possible in the UK?

You are also comparing a technique to handle slack in a long rake of
goods wagons with the operation of relatively short rake of passenger
rolling stock with low slack couplers and a locomotive on each end, not
just the front.

I would be surprised if goods trains in the UK didn't also use the 'power
brake' technique to stop the slack from running in.

Nope, "power braking: is common, even on passenger trains. Even North
America steam used the "power brake" technique.


--
Cheers
Roger T.

Home of the Great Eastern Railway
http://www.highspeedplus.com/~rogertra/

Dangers of High Speed Trains Pushed from the Rear
 

"Nev Arthur"

"Roger T." wrote
It's typical in North America to "power brake". In power braking, the
throttle is left in notch two or three, the independent brake in full
release while the train is brought to a stand with the train brake
working
against the throttle. Is this not possible in the UK?

Not with the stuff I drive. Why would you do that?
Nev

To Keep the slack stretched. Remember, even North American passenger trains
have slack. An inch or so in every coupling between each car.


--
Cheers
Roger T.

Home of the Great Eastern Railway
http://www.highspeedplus.com/~rogertra/

Dangers of High Speed Trains Pushed from the Rear
 

David Hansen wrote:

James Robinson wrote this:

- There is no mention of the power setting in the interim report.

Irrelevant. We know that with the brakes applied traction power
cannot be obtained.

Yes, I'll grant you that.

Yes, it's likely that an emergency application was made, but my point
was that the RI report was not detailed enough to make that clear, and
people are jumping to conclusions.

Beyond that, the other three points I made still stand.

Dangers of High Speed Trains Pushed from the Rear
 

James Robinson writes:
It makes absolutely no difference what the distribution of weight in the
train is when stopping in a hurry. The suggestion that the locomotive in
the rear is somehow a problem demonstrates a complete misunderstanding
of the physics involved.

The issue is the total mass of the train behind a derailed vehicle,
which includes the mass of the coaches as well as the power car. That
total mass is what creates the tendency to jackknife.

Er, this is why it *does* make a difference.

If a passenger car weighs P tons, and a locomotive weighs L tons
(where L P), then moving a single locomotive from the front to
the rear increases the total weight behind the Kth vehicle from the
front of the train by L-P tons; and it increases the total weight
behind the Kth passenger car by L tons.

It is one thing to decide that this difference does not pose enough
additional risk to offset the operational benefits; it is quite another
to say that it makes "absolutely no difference" and throw around words
like "complete misunderstanding" while disproving your own point.

Another issue is whether the heavier locomotive or the lighter passenger
cars would be more likely to derail in any particular situation. If one
type of vehicle is more likely to derail, putting it at the front is a
less safe choice. But I think this would depend on the particular mode
of derailment, and probably on the suspension characteristics of the
individual models; it's not obvious which is the best choice on this
basis, or, again, whether it makes enough difference to offset matters
of operational benefit.
--
Mark Brader, Toronto "As long as that blue light is on, the
computer is safe." -- Hot Millions

My text in this article is in the public domain.

Dangers of High Speed Trains Pushed from the Rear
 

"Roger T." wrote
It's typical in North America to "power brake". In power
braking, the
throttle is left in notch two or three, the independent brake
in full
release while the train is brought to a stand with the train
brake
working
against the throttle. Is this not possible in the UK?

"Nev Arthur"
Not with the stuff I drive. Why would you do that?

To Keep the slack stretched. Remember, even North American
passenger trains
have slack. An inch or so in every coupling between each car.

Ah! See, you're talking to a passenger train driver here! I don't
know of all these tricks of the trade. On a Eurostar if you make
a brake application of more than just a bit, then the power gets
cut off. If the brake is slightly on, you cannot take power
either. That can cause much consternation when the driver hasn't
realised the brake is on slightly.
Nev

Dangers of High Speed Trains Pushed from the Rear
 

"Nev Arthur" wrote in
message ...
"Roger T." wrote
It's typical in North America to "power brake". In power braking, the
throttle is left in notch two or three, the independent brake in full
release while the train is brought to a stand with the train brake
working
against the throttle. Is this not possible in the UK?

"Nev Arthur"
Not with the stuff I drive. Why would you do that?

To Keep the slack stretched. Remember, even North American passenger
trains
have slack. An inch or so in every coupling between each car.

Ah! See, you're talking to a passenger train driver here! I don't know of
all these tricks of the trade. On a Eurostar if you make a brake
application of more than just a bit, then the power gets cut off. If the
brake is slightly on, you cannot take power either. That can cause much
consternation when the driver hasn't realised the brake is on slightly.
Nev

The wonderful traction interlock... Just make sure you don't get problems
with it on MY little railway, Nev- you b****** are bad enough when the snow
gets in the motors. What turns are you on at the moment ?
Brian

Dangers of High Speed Trains Pushed from the Rear
 

"Nev Arthur" wrote
Ah! See, you're talking to a passenger train driver here! I
don't know of all these tricks of the trade. On a Eurostar if
you make a brake application of more than just a bit, then the
power gets cut off. If the brake is slightly on, you cannot
take power either. That can cause much consternation when the
driver hasn't realised the brake is on slightly.

"BH Williams" wrote
The wonderful traction interlock... Just make sure you don't
get problems with it on MY little railway, Nev- you b****** are
bad enough when the snow gets in the motors. What turns are you
on at the moment ?

That's your fault, you keep the Tunnel too warm! ;-)
I'm on the Disney on Monday, 9074 I think, 09.39 out of WIT.
First one back into the UK on Tuesday, about 07.00 on your bit.
That's what's scheduled anyway.
Good luck to you and your colleagues, I know it's a bit miserable
there with the cuts and that. :-(
Nev

Dangers of High Speed Trains Pushed from the Rear
 

Upon the miasma of midnight, a darkling spirit identified as Roger T.
gently breathed:

Irrelevant. We know that with the brakes applied traction power
cannot be obtained.

Does this mean that any brake application automatically cuts traction power?

I believe the systems are set such that as soon as the brake pressure or
vacuum drops (or rises) beyond a certain point, power is automatically
cut and cannot be reapplied until the brake is restored.

It's typical in North America to "power brake". In power braking, the
throttle is left in notch two or three, the independent brake in full
release while the train is brought to a stand with the train brake working
against the throttle. Is this not possible in the UK?

I can see the advantages of this on very long freight trains, even with
continuous brakes there must be a lot of slack in a mile long train, but
your later post said it was common on passenger trains too - any idea
why? I don't see any advantage to it on something like an HST, where
the control layout ensures that brake valves open and shut
simultaneously at front and rear powercars, and there is no slack worth
speaking of in the 8 coach formations. Even in the days of 15 coach Mk1
rakes, it wasn't, AFAIK, possible. Possibly north American couplers
have more slack than UK ones do? The buckeyes fitted as standard from
Mk1 onwards are 3/4 scale copies of the US ones, though, and of course
until just a few years ago (and still, on railtour stock) the loco is
attached via screw-link over the drawhook with buffers extended to take
the compression.

Btw, what is the independent brake? We tend to have straight-air on
locos, and automatic air or automatic vacuum on the train.

--
- Pyromancer Stormshadow.
http://www.inkubus-sukkubus.co.uk -- Pagan Gothic Rock!
http://www.littlematchgirl.co.uk -- Electronic Metal!
http://www.revival.stormshadow.com -- The Gothic Revival.

Dangers of High Speed Trains Pushed from the Rear
 

On Thu, 11 Nov 2004 12:04:55 -0800, Roger T. wrote in
net.com, seen in
misc.transport.rail.europe:

Irrelevant. We know that with the brakes applied traction power
cannot be obtained.

Does this mean that any brake application automatically cuts traction power?

With the 3-step Westcode brake as fitted to Sprinters, any application
of step 2 or higher will automatically cause traction power to be cut
off.

HSTs have 7-step Westcode, so I can't say at which step power will be
cut off - but I'm happy to say that an emergency brake application
will result in traction power being cut off.

--
Ross Hamilton, in Lincoln (UK)
From address *will* bounce

Dangers of High Speed Trains Pushed from the Rear
 

"Pyromancer"

I can see the advantages of this on very long freight trains, even with
continuous brakes there must be a lot of slack in a mile long train, but
your later post said it was common on passenger trains too - any idea
why?

Because North American passenger trains have slack.

Also permits some leeway when travelling really slowly to a stop, you can
keep the train rolling without having to release the brakes to travel that
extra say 20 feet to the correct stopping point.

I used to power brake even with a trains of two passenger cars and even with
the doodlebug, a pre-war railcar. Mid you, in these cases it was power
braking with the throttle in notch one.


--
Cheers
Roger T.

Home of the Great Eastern Railway
http://www.highspeedplus.com/~rogertra/

Dangers of High Speed Trains Pushed from the Rear
 

In message , David Hansen
writes

Does this mean that any brake application automatically cuts traction power?

That is my understanding and it has been stated by others who are in a
position to know. Such an interlock appears to have been common since
the 1960s.
Not on the 6300s, 800s,1000s,7000s,9500s,1600s or any steam engine I
ever worked on.
--
Clive.

Dangers of High Speed Trains Pushed from the Rear
 

On Fri, 12 Nov 2004 01:12:56 +0000 someone who may be Clive Coleman
wrote this:-

Such an interlock appears to have been common since the 1960s.
Not on the 6300s, 800s,1000s,7000s,9500s,1600s or any steam engine I
ever worked on.

Were any of them designed in the late 1950s or 1960s?


--
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I will always explain revoked keys, unless the UK government
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Dangers of High Speed Trains Pushed from the Rear
 

"Nev Arthur" wrote in
message ...
"Nev Arthur" wrote
Ah! See, you're talking to a passenger train driver here! I don't know
of all these tricks of the trade. On a Eurostar if you make a brake
application of more than just a bit, then the power gets cut off. If the
brake is slightly on, you cannot take power either. That can cause much
consternation when the driver hasn't realised the brake is on slightly.

"BH Williams" wrote
The wonderful traction interlock... Just make sure you don't get problems
with it on MY little railway, Nev- you b****** are bad enough when the
snow gets in the motors. What turns are you on at the moment ?

That's your fault, you keep the Tunnel too warm! ;-)
I'm on the Disney on Monday, 9074 I think, 09.39 out of WIT.
First one back into the UK on Tuesday, about 07.00 on your bit.
That's what's scheduled anyway.
Good luck to you and your colleagues, I know it's a bit miserable there
with the cuts and that. :-(
Nev

I'll listen out on the track-to-train for you..(early call both days, but
cover-only on the Monday)
Brian
Brian

Dangers of High Speed Trains Pushed from the Rear
 

"David Hansen" wrote in message
...
On Fri, 12 Nov 2004 01:12:56 +0000 someone who may be Clive Coleman
wrote this:-

Such an interlock appears to have been common since the 1960s.
Not on the 6300s, 800s,1000s,7000s,9500s,1600s or any steam engine I
ever worked on.

Were any of them designed in the late 1950s or 1960s?


--
David Hansen, Edinburgh | PGP email preferred-key number F566DA0E
I will always explain revoked keys, unless the UK government
prevents me by using the RIP Act 2000.


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I don't know if it's significant, but I don't believe any of the classes
that Clive notes were designed for multiple (rather than tandem) operation.
Brian

Dangers of High Speed Trains Pushed from the Rear
 

In message , BH Williams
writes
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I don't know if it's significant, but I don't believe any of the
classes that Clive notes were designed for multiple (rather than
tandem) operation. Brian
I don't think the 1000s or 95s were but certainly the 800s and 63s were
equipped and could work under one driver. The 7000s had different
control equipment, orange triangle if I remember correctly, and again
could be worked from a single cab.
--
Clive Coleman

Dangers of High Speed Trains Pushed from the Rear
 

"Roger T." wrote:

It's typical in North America to "power brake".

Wash your mouth out with soap. That practice is discouraged by the
railway companies, as it wastes fuel. Some railways will even
discipline employees if they power brake.

Dangers of High Speed Trains Pushed from the Rear
 

"Roger T." wrote:

Nope, "power braking: is common, even on passenger trains.

The locomotives used on VIA Rail Canada's transcontinental passenger
train are set up like the HST. i.e., if the air brakes are applied, the
power is automatically shut off. That means the drivers cannot power
brake. Other passenger locomotives will allow power braking, but it is
discouraged.

Dangers of High Speed Trains Pushed from the Rear
 

Pyromancer wrote:

Btw, what is the independent brake? We tend to have straight-air on
locos, and automatic air or automatic vacuum on the train.

North American locomotives have a dual braking system. The straight air
system is called the independent brake, since it can be applied
independently of the brake on the rest of the train. Locomotive brakes
will also apply with an automatic brake application.

In typical freight train operation, the driver will "bail off". or
release, the automatic brake application to reduce wheel heating. If
the driver is otherwise incapacitated, the brakes will apply. On
shorter trains, like passenger trains, the driver will typically bail
off the automatic application, then apply a partial application of the
independent, straight air brake to assist in reducing train speeds.

Dangers of High Speed Trains Pushed from the Rear
 

James Robinson wrote:
"Roger T." wrote:

Nope, "power braking: is common, even on passenger trains.


The locomotives used on VIA Rail Canada's transcontinental passenger
train are set up like the HST. i.e., if the air brakes are applied, the
power is automatically shut off. That means the drivers cannot power
brake. Other passenger locomotives will allow power braking, but it is
discouraged.

With the possible exception of the auto train, I believe VIA's
transcontinental train is the longest passenger train in North America.
If power braking isn't needed on that train, then itn't likely to
be needed on very many passenger trains.

Greg Gritton

Dangers of High Speed Trains Pushed from the Rear
 

"James Robinson" wrote in message
...
"Roger T." wrote:

Nope, "power braking: is common, even on passenger trains.

The locomotives used on VIA Rail Canada's transcontinental passenger
train are set up like the HST. i.e., if the air brakes are applied, the
power is automatically shut off. That means the drivers cannot power
brake. Other passenger locomotives will allow power braking, but it is
discouraged.

Didn't know about the newer VIA locos.


--
Cheers
Roger T.

Home of the Great Eastern Railway
http://www.highspeedplus.com/~rogertra/

Dangers of High Speed Trains Pushed from the Rear
 

On Wed, 10 Nov 2004 18:10:58 UTC, David Hansen
wrote:

: The forces the power cars produce are minor compared
: to the forces involved in a crash.

3000hp at 100mph is pretty close to 5 tons of thrust. As David says,
compared to the crash forces on half a train (4 * 35 ton coaches + 1 *
70 ton locomotive = 210 tons), that's trivial.

Ian

--

Dangers of High Speed Trains Pushed from the Rear
 

On Wed, 10 Nov 2004 22:20:42 UTC, Pyromancer
wrote:

: Stopping 350 tons in such a short space requires the
: dissipation of a great deal of energy

350 tons at 100mph (45 m/s) is 1/2 * 350 * (45)^2 = 350MJ which is the
same amount you get if you dropped the entire train from a height of
100m (three hundred feet). Or, if you prefer, 84 kilograms of TNT.

Ian
--

Dangers of High Speed Trains Pushed from the Rear
 

"Ian Johnston" wrote in message
...
3000hp at 100mph is pretty close to 5 tons of thrust. As David says,
compared to the crash forces on half a train (4 * 35 ton coaches + 1 *
70 ton locomotive = 210 tons), that's trivial.

Actually it's even more trivial than that, because the power car's engine
only produces 2250hp, of which (according to a general rule of thumb for
diesel locos) only about 80% would be available for traction even if not
providing ETS. So we are probably looking at 1600-1800hp available for
traction, depending on the ETS load, reducing the calculated thrust to
around 3 tons.

That's still higher than my guess yesterday (2 tons), but that was just a
guess which I thought afterwards might have been a bit on the low side.

Roger

Dangers of High Speed Trains Pushed from the Rear
 

Greg Gritton schrieb:

Nope, "power braking: is common, even on passenger trains.


The locomotives used on VIA Rail Canada's transcontinental passenger
train are set up like the HST. i.e., if the air brakes are applied, the
power is automatically shut off. That means the drivers cannot power
brake. Other passenger locomotives will allow power braking, but it is
discouraged.

With the possible exception of the auto train, I believe VIA's
transcontinental train is the longest passenger train in North America.

How long is it?

Regards, ULF

Dangers of High Speed Trains Pushed from the Rear
 

"Richard J." schrieb:

The unfounded idea that the rear power car was still under full power
was certainly NOT in the interim HSE report. It was an ignorant rumour
that I believe was mentioned first on Sky News a few hours after the
crash.

We had the same rumour after the Eschede crash.

Regards, ULF

Dangers of High Speed Trains Pushed from the Rear
 

In article ,
(Ulf Kutzner) wrote:

"Richard J." schrieb:

The unfounded idea that the rear power car was still under full power
was certainly NOT in the interim HSE report. It was an ignorant
rumour that I believe was mentioned first on Sky News a few hours
after the crash.

We had the same rumour after the Eschede crash.

Er, that was the classic unstoppable train bringing down an overbridge and
so meeting the immovable object.

--
Colin Rosenstiel

Dangers of High Speed Trains Pushed from the Rear
 

Roger T. wrote:
"Nev Arthur"
"Roger T." wrote
It's typical in North America to "power brake". In power braking, the
throttle is left in notch two or three, the independent brake in full
release while the train is brought to a stand with the train brake
working against the throttle. Is this not possible in the UK?

Not with the stuff I drive. Why would you do that?
Nev

To Keep the slack stretched. Remember, even North American passenger trains
have slack. An inch or so in every coupling between each car.

What's the point in having slack if you keep it stretched?

Dangers of High Speed Trains Pushed from the Rear
 

"Aidan Stanger" wrote in message
...
Roger T. wrote:
"Nev Arthur"
"Roger T." wrote
It's typical in North America to "power brake". In power braking, the
throttle is left in notch two or three, the independent brake in full
release while the train is brought to a stand with the train brake
working against the throttle. Is this not possible in the UK?

Not with the stuff I drive. Why would you do that?
Nev

To Keep the slack stretched. Remember, even North American passenger
trains
have slack. An inch or so in every coupling between each car.

What's the point in having slack if you keep it stretched?

Because if there was no slack there would be nothing too stretch!!

Dangers of High Speed Trains Pushed from the Rear
 

Brimstone wrote:
"Aidan Stanger" wrote...
Roger T. wrote:
"Nev Arthur"
"Roger T." wrote
It's typical in North America to "power brake". In power braking, the
throttle is left in notch two or three, the independent brake in full
release while the train is brought to a stand with the train brake
working against the throttle. Is this not possible in the UK?

Not with the stuff I drive. Why would you do that?
Nev

To Keep the slack stretched. Remember, even North American passenger
trains
have slack. An inch or so in every coupling between each car.

What's the point in having slack if you keep it stretched?

Because if there was no slack there would be nothing too stretch!!

Surely being able to stretch it could not possibly be the reason for
having it?

Dangers of High Speed Trains Pushed from the Rear
 

Aidan Stanger wrote:

It's typical in North America to "power brake". In power braking, the
throttle is left in notch two or three, the independent brake in full
release while the train is brought to a stand with the train brake
working against the throttle. Is this not possible in the UK?

Not with the stuff I drive. Why would you do that?
Nev

To Keep the slack stretched. Remember, even North American passenger
trains
have slack. An inch or so in every coupling between each car.


What's the point in having slack if you keep it stretched?

Because if there was no slack there would be nothing too stretch!!


Surely being able to stretch it could not possibly be the reason for
having it?

If the train driver (uh, "engineer") weren't powering against the
brakes he would be in danger of being hauled before the House
un-American Affairs Committee on charges of using less than the
the minimum mandated patriotic daily fossil fuel quota.

Dangers of High Speed Trains Pushed from the Rear
 

"Richard Mlynarik"

If the train driver (uh, "engineer") weren't powering against the
brakes he would be in danger of being hauled before the Heouse
un-American Affairs Committe on charges of using less than the
the minimum mandated patriotic daily fossil fuel quota.

Why would a Canadian, Mexican or Caribbean engineer be hauled before the
"Heouse
un-American Affairs Committe"? sic.

I did say "North American" engineers. :-)


--
Cheers
Roger T.

Home of the Great Eastern Railway
(Site now back up and working)
http://www.highspeedplus.com/~rogertra/

Dangers of High Speed Trains Pushed from the Rear
 

Mark Brader wrote:

James Robinson writes:

It makes absolutely no difference what the distribution of weight in the
train is when stopping in a hurry. The suggestion that the locomotive in
the rear is somehow a problem demonstrates a complete misunderstanding
of the physics involved.

The issue is the total mass of the train behind a derailed vehicle,
which includes the mass of the coaches as well as the power car. That
total mass is what creates the tendency to jackknife.

Er, this is why it *does* make a difference.

If a passenger car weighs P tons, and a locomotive weighs L tons
(where L P), then moving a single locomotive from the front to
the rear increases the total weight behind the Kth vehicle from the
front of the train by L-P tons; and it increases the total weight
behind the Kth passenger car by L tons.

My response was hyperbole, to some extent. I was addressing the
descriptions in the press that focus on the big nasty power car at the
rear of the train, and ignore the fact that the leading carriage had 7
other carriages behind it in addition to the power car.

The power car was not some sort of juggernaut that pushed everything
ahead of it hither and yon, only additional mass that adds to the
momentum behind the leading carriage. To suggest otherwise is to
suggest that trains made up of anything in excess of 8 or 9 carriages
is somehow unsafe.

It is the very essence of what a train is -- a series of vehicles
coupled together. To ascribe the extent of the derailment solely to
the fact that a power car is marshalled at the rear, which some
reports did, demonstrates a misunderstanding of the physics.

Does it mean that the mass from additional carriages are somehow
better than the equivalent mass of a power car? Should trains be
limited in length to a maximum of two carriages, since the additional
mass of one more carraige behind the leading one would cross a
threshold of safety and become unsafe? Would those who advocate the
removal of the trailing power car reverse their views after a tail-end
collision and demand the additional protection of the power car again?

It is one thing to decide that this difference does not pose enough
additional risk to offset the operational benefits; it is quite another
to say that it makes "absolutely no difference" and throw around words
like "complete misunderstanding" while disproving your own point.

The media reports, plus those of many posters to this group
demonstrate a complete misunderstanding of the physics, and ascribe
far more risk to the operation of locomotives at the rear of trains
than is reality.

However, let me rephrase my original statement to reduce the
controversy: Given the many factors involved in collisions and
derailments, the effect of placing a power car at the rear of the
train on the severity of the resulting accident, in comparison to
other factors, is so small as to be inconsequential, or presents no
greater risk than other generally accepted operating practices. Is
that run-on sentence mushy enough?