Increased risk travelling North or South?

[richscylla]

If I am on a train travelling from Leeds to London with a 91 supplying the power is there more risk of of a bigger accident that if travelling North?

What I'm really asking is, is there any significant increase in risk in the unlikely event of an accident if the power car is pushing rather than pulling the rolling stock?

 

[DarloRich]

If I am on a train travelling from Leeds to London with a 91 supplying the power is there more risk of of a bigger accident that if travelling North?

What I'm really asking is, is there any significant increase in risk in the unlikely event of an accident if the power car is pushing rather than pulling the rolling stock?

eh? does it matter?

 

[dk1]

We run a very very safe railway these days. DVTs are weighted so you should be fine. I wouldnt risk myself driving them otherwise.

 

[richscylla]

I'm just interested if it makes a difference. Surely there is quite a difference when it comes to the physics of a situation.

 

[yorkie]

What I'm really asking is, is there any significant increase in risk in the unlikely event of an accident if the power car is pushing rather than pulling the rolling stock?

No.

eh? does it matter?

In a minuscule number of cases, potentially yes.

http://www.railwaysarchive.co.uk/eventsummary.php?eventID=150
http://en.wikipedia.org/wiki/Polmont_rail_accident

....the front end was lighter than the rear and had the risk of being pushed over an obstruction, leading to derailment...

So yes in such cases it is safer to be loco hauled, rather than be on a multiple unit, or loco propelling.

However I very much doubt the following would apply...

The dynamics of the train, with the locomotive pushing from behind, meant that when the brakes were applied from the DBSO at the front there was a delay in transmission of the signal to the locomotive brakes in order to prevent a sudden backlash to the carriages in front;[7] this caused the train to decelerate only slightly

... as I am pretty sure that there would be no such delay with a Class 91 & Mk4 set today (but I am sure an expert will be along shortly to confirm....!)

 

[richscylla]

Maybe I shouldn't have made it such a safety based question, I'm not actually nervous about the incident. Just wondered if there were any differences or differing factors having a power car a few hundred meters behind the driver. For example weighting in DVTs which I didn't know about.

 

[DarloRich]

@ Yorkie - i meant a crash is a crash. That is the most important point, not the formation of the train!

 

[richscylla]

No.


In a minuscule number of cases, potentially yes.

http://www.railwaysarchive.co.uk/eventsummary.php?eventID=150
http://en.wikipedia.org/wiki/Polmont_rail_accident

So yes in such cases it is safer to be loco hauled, rather than be on a multiple unit, or loco propelling.

However I very much doubt the following would apply...

... as I am pretty sure that there would be no such delay with a Class 91 & Mk4 set today (but I am sure an expert will be along shortly to confirm....!)

Thanks Yorkie, reading these links is exactly what was interested in.

 

[yorkie]

@ Yorkie - i meant a crash is a crash. That is the most important point, not the formation of the train!

A crash is incredibly unlikely, and a crash where it makes a difference even more so, but in some rare cases it could be safer to have a loco at the front.

But that's not to say that such a tiny risk could be used as justification for having a loco at the front of each train of course, as that would be totally disproportionate.

 

[edwin_m]

A push-pull set with the loco at the rear is arguably more risky than a MU set, because if the front part derails or hits something it will decelerate rapidly and the momentum of the loco sets up a compressive force through the train. However, as stated by others, these types of accident are very rare and the consequences of each are down to a wide range of essentially random factors. So I'd be quite happy sitting in a 225 set in either direction knowing that I was approximately ten times safer than if I'd been in a car.

 

[455driver]

So I'd be quite happy sitting in a 225 set in either direction knowing that I was approximately 10 times safer than if I'd been in a car.

And the rest!

I reckon you can add a couple of zeros (at least) on the end of that 10.

 

[martybabes]

And the rest!

I reckon you can add a couple of zeros (at least) on the end of that 10.

But we're not comparing rail travel with car travel. We are discussing whether it is safer to be pushed or pulled.

 

[455driver]

It is safer to be pulled but the difference is so small (in the grand scheme) to be infinitesimal.

Now why cant they build a train that has a locomotive at either end so you are always being pulled?

 

[Gwenllian2001]

It is safer to be pulled but the difference is so small (in the grand scheme) to be infinitesimal.

Now why cant they build a train that has a locomotive at either end so you are always being pulled?

It's called HST.

 

[455driver]

It's called HST.

I know, hence the on the end.

 

[deltic1989]

It's called HST.

In an HST aren't you being pulled and pushed at the same time? As I understand it both power cars are providing power.
I remember hearing that it was this configuration that contributed to the sets involved in the Southall and Ladbroke Grove incidents to compress in the way they did, because the front power car decelerated suddenly but the rear power car was still pushing.

 

[broadgage]

Common sense and basic physics suggests that having the locomotive at the front is slightly safer in the event of accident.
However do not count on statistics confirming this ! fatal accidents are very rare, and the "sample size" is therefore too small for collected figures to give an indication of the relative risks.

If a dozen lives were lost in an accident with loco leading, this would skew the average figures for years, even for decades, and give the misleading impression that loco at the front was less safe, when in fact the accident might have been caused by some freak circumstance never to be repeated with position of the loco being irelevant.

Consider an analogy of fatal house fires.
Suppose a developer builds an estate of 400 similar houses, about half with odd house numbers and half with even.
After a few years, 2 of the odd numbered houses have burnt, each with the loss of several lives, but no even numbered houses have burnt.
Does this prove that houses with odd numbers are at greater risk of fire ?

 

[pablo]

If you're worried about north-south, I wouldn't try east-west. :eek:

 

[Deerfold]

If you're worried about north-south, I wouldn't try east-west. :eek:

I'm only going to worry about that when someone suggests putting the loco on a parallel track next to the train I'm on...

 

[snowball]

In an HST aren't you being pulled and pushed at the same time? As I understand it both power cars are providing power.
I remember hearing that it was this configuration that contributed to the sets involved in the Southall and Ladbroke Grove incidents to compress in the way they did, because the front power car decelerated suddenly but the rear power car was still pushing.

In normal running, if both power cars are contributing equally to the traction, then if you work it out, couplings near the front are in tension, those near the back are in compression, and those in the middle are neutral.

If the brakes are applied and it takes time for brake effort to spread from front to back, this will no longer apply.

 

[route:oxford]

If I am on a train travelling from Leeds to London with a 91 supplying the power is there more risk of of a bigger accident that if travelling North?

What I'm really asking is, is there any significant increase in risk in the unlikely event of an accident if the power car is pushing rather than pulling the rolling stock?

Depends on the accident...

A bridge is more likely to collapse under the strain of a heavy locomotive than the weight of a DVT & Mk4...

So if you were at the front of a propelled train, you'd be less likely to be killed by drowning in the raging torrent below than the people in the carriage next to the loco...

 

[daikilo]

In normal running, if both power cars are contributing equally to the traction, then if you work it out, couplings near the front are in tension, those near the back are in compression, and those in the middle are neutral.

If the brakes are applied and it takes time for brake effort to spread from front to back, this will no longer apply.

You are not wrong, but only the front power car will be subject to significant aerodynamic resistance which could mean that most of the couplers will actually be under compression from the rear power car.

To get back to the subject, the real issue is the kinetic energy. If e.g. a 225 hits a car on a crossing, it will matter little if the DVT or the 91 are leading. If however, e.g the train derails, hits a concrete bridge support which does not collapse then the way the kinetic energy of individual vehichles is absorbed/redirected will become relevant, such as the way they then derail, which may be sideways and not an end-on compression.

What is of essence is that this has been taken into account in DVT design since the initial Scotrail ballasted Mk2s. The design requirements are to meet safety criteria when in both DVT-leading and power-car leading modes.

The design requirements for other safety systems like signals and junctions are to eliminate derailments and crashes.

If this is a real problem for you then I suggest that when you are in a train with DVT leading you aim for about coach 5 or 6. My logic is that in the concrete block case there is a reasonable chance that kinetic energy will have resulted in some jack-knifing and forces on your coach will be totally survivable. I am not saying that they will not be in other coaches.

Have you ever seen the result of a car crash with a closing speed of e.g 100mph? Probably not as you wouldn't even think about asking the question you did.

 

[colchesterken]

It dont work on the Hornby 00 in the loft, pushing they always Jack-knife on the bends or points

 

[6Gman]

It is safer to be pulled but the difference is so small (in the grand scheme) to be infinitesimal.

:

There are a number of factors which affect level of risk e.g. sitting at a window seat is more dangerous than an aisle seat; forward facing more dangerous than rear facing etc

But the level of risk is so, so low that it doesn't stop me preferring a facing window seat!

 

[Flying Snail]

It dont work on the Hornby 00 in the loft, pushing they always Jack-knife on the bends or points

In order to make sets fit in reasonably small spaces the curve and point radius' are far more severe than an accurate scale representation. Added to this is the couplers being connected to the bogies rather than the bodies in order to deal with the tight curves.

 

[sprinterguy]

It dont work on the Hornby 00 in the loft, pushing they always Jack-knife on the bends or points

There's little reason why they should be doing this: I successfully ran Hornby Intercity 225s, 90s and mark 3s and HSTs (Seeing as only one power car is motorised in 00 gauge) in propelling mode on my layout for years with no mishaps.

 

[455driver]

There's little reason why they should be doing this: I successfully ran Hornby Intercity 225s, 90s and mark 3s and HSTs (Seeing as only one power car is motorised in 00 gauge) in propelling mode on my layout for years with no mishaps.

Poor driving technique!

 

[martybabes]

Since when has "propel" meant push?

 

[edwin_m]

Since when has "propel" meant push?

Standard rule book terminology for a many years.

 

[MK Tom]

Should note when talking about how the physics works at OO scale, even if you weighted the vehicles all to scale and built them as perfect scale replicas down to the coupling, the physics would still operate differently due to scale and weight. Like how spiders survive insanely long drops. Obviously all the same laws apply but the effect is different for all manner of reasons. But Hornby DVTs aren't as heavy as real ones in comparison to the locos and carriages anyway.

Wasn't the power from the rear loco a major factor in Ufton Nervett? Causing the centre carriages to jackknife the way they did.