Railroad Forums 

Discussion relating to the operations of MTA MetroNorth Railroad including west of Hudson operations and discussion of CtDOT sponsored rail operations such as Shore Line East and the Springfield to New Haven Hartford Line

Moderators: GirlOnTheTrain, nomis, FL9AC, Jeff Smith

 #1232494  by Trainer
 
Push and pull are likely equally safe but where the engine is arranged does have an impact on the physics of an accident. It is quite possible that had the heavy locomotive been first in our most recent accident, the momentum induced by its heavy weight may have sailed it into the river along with several cars behind it, and this tragedy would have had an extra dimension to deal with. As it happened, the engine weight may have acted like a brake to the other cars.

"Safer" push or pull one way or another hinges on the exact circumstances of the track conditions, curve, speed, number of cars, and surrounding terrain of the specific circumstances. I suspect that the physics balances out in the long run as to which is "better".
 #1232497  by Clean Cab
 
DutchRailnut wrote:The real experts seem to believe push-pull is safe, as today 35 000 trains a day are operated this way and testing by international agencies and domestic NTSB do seem to suggest that push-pull is safe.
only non-experts seem to think its un-safe !!
Agreed!! There is nothing unsafe about having an engine push rather than pull a train. The notion that the heavier engines pushes the train with more mass making it uncontrollable is insane and only advocated by those who are uniformed. The engine brakes at the same rate as the cars it is shoving. For me, my only concern operating a push/pull train from the cab car was how exposed I was to striking debris. If I was on an engine, I'd be up higher and protected by a lot more material.
 #1232501  by Patrick Boylan
 
8th Notch wrote:
Patrick Boylan wrote: http://usnews.nbcnews.com/_news/2013/12 ... in-ny?lite" onclick="window.open(this.href);return false;
Sources told NBC News late Sunday afternoon that the train's engineer — a "respected veteran" with 20 years of Metro-North experience who suffered minor injuries — claimed when first responders arrived that he hit the brakes as the train approached the turn.
Sounds like more speculation again to me.... As stated we don't know any of the facts! We are all human and regardless of how many times the track was traveled by the engineer he still could have not been paying attention or lost situational awareness. Obviously as a railroader we are all hoping for his sake that it wasn't human error however as humans we are all subject to it in some way shape or form. The control car does not send a signal to the locomotive telling it it to apply the brakes on the train, it is done pneumatically from the brake valve in the control car itself. Not a knock against anyone but like Dutch said only non experts think push pull is unsafe and I think that is because many do not know how it works. If a train derails and goes into emergency it also trips a pneumatic control switch which in turn knocks down any power being supplied from the loco.
I hope you meant we don't know ALL the facts, not that we don't know ANY. We know some of the facts. It's a fact that some reporter said that some sources said the engineer said he hit the brakes. It's a fact I know from looking at the pictures that the entire train came off the tracks without tearing up the tracks as much as the New Haven line's derailment and sideswipe did.

I also know that the control car pneumatically controls the brakes, but that's just another way of sending a signal, whether it's electronic, pneumatic or carrier pigeon. Turning a handle in the cab car is supposed to apply brakes throughout the train, or apply brakes in the locomotive only, and another handle is supposed to control the throttle.
The further away the handles are from the things that they're supposed to control, the more likely it is that something will go wrong.

Yes, if a train derails and goes into emergency it trips a pneumatic switch and the locomotive's supposed to stop pushing, or pulling, and all the brakes are supposed to go on. But if there was a problem with the system in the first place MAYBE, and yes this is speculation, the engineer didn't get the brake application he was expecting, and so the train didn't slow down the way it should have BEFORE it derailed. And if the locomotive's at the back you've added several extra connection points between the control stand and the locomotive.
Haven't we all heard of cases where the last few cars in a freight train didn't apply their brakes because of cumulative air line problems? So what happens if there's a bit of blockage in the air line from cab car to locomotive, can it keep the cab car's brake valve from sending a proper signal to the locomotive? And vice versa, does trying to apply trainline brakes from the locomotive ever have trouble getting all the cars to apply brakes? What brake did the engineer try to apply, locomotive only, or brakes on the entire train? I don't have these facts, for all I know the engineer might not be able to choose locomotive brake only, maybe this equipment has some fancy stuff that tries to decide for the engineer what the best blend of locomotive and train brake is.
DutchRailnut wrote:The real experts seem to believe push-pull is safe, as today 35 000 trains a day are operated this way and testing by international agencies and domestic NTSB do seem to suggest that push-pull is safe.
only non-experts seem to think its un-safe !!
Dutch, I haven't said that locomotive on the rear is more dangerous than in the front, I've only said I wonder, and despite you saying it twice just the fact that "everybody does it" means a lot less than the testing you say has been done.

I do find Mbta fan's example interesting, where locomotive in the rear may have been a mitigating factor in that rear end crash.
 #1232508  by s4ny
 
Admin note: let's keep the quality commentary to a minimum, i.e. zip. It's a valid discussion, no matter the viewpoint. The member is not asking about extending the 7 train to Mars, they are asking a physics question. Whether the NTSB takes this into account remains to be seen for months.

I've edited the idiot posts out. Reminder: do not engage in or respond to this type of commentary. Apologies to this member.


Well, here we go with the name calling again. It is an honor to be in the midst of
such intelligent people.

If the brakes are controlled by the engineer in the front car with the locomotive
pushing, what happens if the front car gets disconnected from the rest of the train?
How does that signal to stop get to the locomotive?

It appears from the jackknifed cars that the locomotive kept pushing until it left
the tracks and fell over.

Why are some members here so virulent in their support of push pull?
 #1232510  by CNJGeep
 
Because there's nothing wrong with it as has been mentioned multiple times in this thread alone? Let's say MN gets rid of push-pull. How would engines be turned and be turned in the same amount of time that it takes for the engineer to walk to the cab car, do a brake test and go? Sometimes that's all the time you have. Show your math. I'll wait.
 #1232521  by ACeInTheHole
 
Lets be realistic. This train didnt merely jump a track, it went off its track, and then proceeded to go straight across another one.. Punching right through two third rails as though they were toothpicks. And the cab car didnt stop sliding until it was almost in the Harlem. That train was going off the track regardless of whether the cab car or locomotive was leading. In fact, if the loco was leading, its extra momentum on the front might very well have dragged the train into the river, rather than causing the drawbar on the fourth car to break, thus stopping the rear three cars from getting too bent out of shape. Each accident is different. Its one thing if several trains a day running in push pull were crashing left and right, but theyre not. Not to desensitize things but its only once every few years or so if that. A train wreck is a rare occurence. Let's get real here.
Last edited by ACeInTheHole on Mon Dec 02, 2013 10:48 am, edited 3 times in total.
 #1232528  by s4ny
 
beanbag wrote:Lets be realistic. This train didnt merely jump a track, it went off its track, and then proceeded to go straight across another one.. Punching right through two third rails as though they were toothpicks. And the cab car didnt stop sliding until it was almost in the Harlem. That train was going off the track regardless of whether the cab car or locomotive was leading. IV fact, if the loco was leading, its extra momentum on the front might very well have dragged the train into the river, rather than breaking the drawbar on the fourth car and stopping the rear three from getting too bent out of shape. Each accident is different. Its one thing if several trains a day running in push pull were crashing left and right, but theyre not. Not to desensitize things but its only once every few years or so if that. A train wreck is a rare occurence. Let's get real here.
Pushing doesn't increase the frequency of accidents. When the locomotive is pushing a train, there will be instances where the severity of the accident will be greater.

In this instance, the train was going too fast for the curve, derailed, and it appears that the locomotive kept on pushing. I am sure there will be simulations that will provide better information including what the accident would have been like if the locomotive had been pulling the train.
 #1232530  by Tommy Meehan
 
s4ny wrote:...it appears that the locomotive kept on pushing...
What makes you think that?
 #1232532  by NH2060
 
Tommy Meehan wrote:
s4ny wrote:...it appears that the locomotive kept on pushing...
What makes you think that?
Probably because the way the middle coach came to a rest zig zagged across the tracks can give the impression that the engine perhaps did keep pushing the consist before it flipped over.
 #1232533  by Jeff Smith
 
s4ny this is the thought I was just having. The operation of push doesn't cause a derailment. In a pull operation, it would seem to be logical that the cars will follow straight and then accordion behind the locomotive as it decelerates after a derailment, especially if suddenly. In a push operation, it seems the engine may continue to push the cars forward and then aside, also in an accordion effect, until it also derails and decelerates.

What is the effect of the difference? I'm not sure. If the engine were in the front in this case, would those 4 people still have died? It seems likely. I'm sure there are computer simulations out there that would take these factors in consideration. It's a worthwhile discussion, though, even if the differences are negligible. I find it informative.

Let's leave the discussion of the accident to the accident thread, and the theory of push-pull here. And please, all, let's leave the flames on the grill.
 #1232536  by p42thedowneaster
 
I agree with the general statement that push pull braking should be as safe as locomotive pulled trains. However, if you observe the KISS rule, you have to admit there is more that could go wrong.
If you're in the locomotive, you can definetely throttle down and access independent locomotive braking.

My true concern with push pull involves the physics of actively pushing (applying power). When you're accelerating or pushing harder to negotiate a hill or curve, at some point the cars will hunt on the rails, perhaps relying on the flanges to hold them in the right direction. Envision the train having rubber wheeled tires instead of tapered, flanged wheels. How far would you get pushing the cars down the road until disaster? As soon as a wheelset hits a bump or eneven spot in the pavement, the cars would send off in different directions. However, this same tram could be pulled and stopped with no problems.

Solution: Simply Slow Down!
The commuter train is already a heavily subsidized luxury option, so why not slow it down a bit? Save fuel, save steel, extend service life of equipment, make crossings and station platforms safer, reduce noise, improve reliability, and allow for longer trains. In return, improve onboard services, repair or improve seating, add faster wifi, restrooms, and vending services if needed. With stations so close together, having a 30-35mph top speed would make very little affect on most schedules.

If you're running an express maybe it makes sense to have a loco on both ends?
Last edited by p42thedowneaster on Mon Dec 02, 2013 11:08 am, edited 1 time in total.
 #1232537  by s4ny
 
Tommy Meehan wrote:
s4ny wrote:...it appears that the locomotive kept on pushing...
What makes you think that?
That is my first impression when looking at the jackknifed cars. Similar to
what happens when you push on a string.
 #1232548  by Tommy Meehan
 
Because a coach landed sideways on the tracks that indicates the engine was still pushing? In a derailment don't cars always wind up jack-knifed? To me the photo looks like the fourth car wound up the way it did because of where the cars ahead stopped.

Btw, this is also why people get angry. Who here is truly competent to interpret what happened with the locomotive from looking at a photo? If a trained railroad accident investigator makes statements based on looking at a photo than you have to consider it. The irony is, people like that are usually much more reserved in making judgements based on rudimentary evidence.

The railroaders say when a push/pull train goes into emergency a pneumatic valve cuts power to the locomotive. That's an air valve. That's sounds like a pretty basic system. It's the same thing when people were writing that the cab car sends a signal to the locomotive to activate the brakes. That's baloney. The cab car has a brake handle. When the engineer moves the handle it opens a valve that releases air from the brake line. When the engineer opens the brake handle in a cab car you can hear the air escaping. This isn't rocket science.

As for the people who died, do we even know that they were in the head car? It sounds like three of them were ejected from the train through broken windows. Did windows only break in the cab car?

It's also possible if the locomotive was leading the locomotive might've stopped faster than the lead coach and then the cars behind would pile up. People died that way in Chatsworth.
Last edited by Tommy Meehan on Mon Dec 02, 2013 11:31 am, edited 1 time in total.
 #1232549  by Ridgefielder
 
NH2060 wrote:
Tommy Meehan wrote:
s4ny wrote:...it appears that the locomotive kept on pushing...
What makes you think that?
Probably because the way the middle coach came to a rest zig zagged across the tracks can give the impression that the engine perhaps did keep pushing the consist before it flipped over.
I just figured that's simple physics. A Shoreliner weighs something like 100k lbs. A P32AC-DM weighs 274k lbs. Once the train hits the dirt, of course it's going to take the locomotive longer to skid to a stop than the passenger cars-- it weighs 2.75x as much.