For Engineers: If you drop the brake will you fall off the road?

Question

Hi Guys,

Further to the question about whether you'd drop the brake before hitting something or "wait for the clang", a couple of you said that dropping the brake would risk a derailment. I was curious to know why this would be.

As a driver myself, this strikes me as a very unsafe method of working. I would be very nervous about taking out any train if there was a risk this might happen. I would want to know that I can give it the lot safely and without the risk of a wreck.

What are your thoughts and experiences?

Answer 1

Force levels are the bugga-boo.

When a moving train is placed into emergency, there are several factors at play that can cause excessive forces to run through the train:

1.  The heavy brake application itself is a problem.  As Andy pointed out, train make-up, with loads and empties scattered through the train, and when taking into account empties will stop in 1/3 the distance of a loaded car, immediately we have cars that want to begin moving at different speeds.  Their interaction with each other is unpredictable.

2.  When placing a train into emergency, power to the locomotives is automatically shut off.  In addition, dynamic brake will be nullified in most instances, in some cases after a delay.  When losing power or dynamic brake, you lose your ability to control slack action.  Keep in mind on long trains, there is to be found 120 feet or more of slack in the train, meaning the head-end will start and stop 120 feet or more before the rear end does.  Bad enough all by itself, but here you now have no slack control with all the cars in your train wanting to move at different speeds.  This causes an "accordion" like effect running through the train.

3.  As the uncontrolled slack is flailing about, the force levels are imparted either to the drafu gear, trucks, roadbed or all three.  The train can separate, with the separated portion crashing into the other.  A drawbar can be pulled out, sometimes digging into the roadbed, derailing equipment behind it.  L/V forces spike.  L/V is the ratio between the vertical force (gravity) and lateral forces (centrifugal and centripital).  If L becomes .9 of V or greater, the wheels of the cars will climb the rail on the outside of a curve due to "jack-knifing" or be pulled off the inside of a curve due to "string-lining."

This is all in additon to the danger of derailment presented by whatever it is that is going to be struck.

I am not attuned to most overseas operations but these things are very real considerations for trains in North America due to their phenomenal mass and length.  Where shorter, lighter trains are in the mix, there is less concern and somewhat reduced danger.

As far as the original question that sparked this, what I consider to be an important exchange of ideas, some engineers will dump the air immediately before hitting a vehicle or pedestrian.  It might make ya feel better, but it changes nothing and the results can be far more reaching than imminent death right ahead of the engine.

People must begin to realize it is not just THEIR lfe that they are gambling when on or near the tracks and disregard good safety practices.  This is why all enginemen and trainmen who contribute here keep hammering away on these very important safety issues because, thus far, some people just don't get it.

It's horrific, but if they ever saw someone's brains spattered against the pilot of a locomotive as I have, bits of flesh, grey matter and hair, they might become more aware.

Answer 2

Thank your for your input, always nice to hear from others that have different experiences to share.

Excellent answers above, I cant add much except to clarify one point, the biggest chance of a train derailing or being torn in two is not from the collision impact but the in-train forces as the slack adjusts, either bunching or stretching very fast.

The same forces are there if we expereince an air hose seperation that puts the train into emergency and I think most of us have had a train torn apart during that secnario. As for causing a derailment, with a large train the danger is always there, that's not to say it happens every time but it is somethign that is always forefront in your mind during an emergency situation.

to be honest, coprorate greed has pushed our train sizes beyond the point where we as engineers are in complete control 100% of the time (just my opinion) others may disagree.

Answer 3

The answer here is correct.  Even in training it is taught that you not put the train into emergency untill you actually hit whatever it is.  If you keep the train tight and hit something and then put the train into emergency you will keep it stretched out. On the other hand if you put the train into emergency before you hit it, and it is a pretty big object, then you run the risk out derailing the train, since all of your slack is already in there is no where for the energy to go to, except out.

Answer 4

It's a matter of train makeup and track.There used to be more strict rules about how trains were built with regards as to where empty cars are placed in the train.But if you have a big block of loaded heavy cars at the rear and a very light empty such as a flat car towards the head end you run the risk of the flatcar being "squirted out" by excess buff forces(especially if the light car happens to be on a curve).If your running stretched and go into emergency normally you'd bail the engines brakes to control slack action and usually there would be no problem.But if your in danger of hitting something and you plug it your probably going to be diving for the floor and not worrying about slack action.Then the buff forces could cause bad things to happen.