1
$\begingroup$

Today I heard a claim that the recently derailed train in Ohio was physically incapable of stopping except at its normal stops.

I am skeptical of that claim because:

  • Normally a vehicle contains whatever hardware it needs to stop. Cars have brakes. Airplanes have wheel brakes and sometimes also thrust reversal, etc. For a vehicle to not contain any mechanism to stop itself seems odd.
  • I cannot think how a train lacking such hardware could be safely operated unless the track contains hardware to slow the train.

To me the idea seems far fetched but I'm an electrical engineer, not mechanical, so it only seemed fitting to ask people who know more about mechanical things than I do.

I understand that trains take a long time to brake. This question is not how long does a train need to stop, why can't trains stop quickly, etc. I understand both of those. This question is about whether freight trains can normally stop themselves faster than merely coasting to a stop, which, as is common knowledge, takes a long time.

That is why I worded the question the way that I did. Is it normal for a freight train to require some kind of external device, be it part of the track or something else, in order to stop? Or is the idea a lot rot?

$\endgroup$
1
  • $\begingroup$ As expressed, this could mean that the "normal stops" were close enough together, and the train heavy enough, that, in order to stop at the nth normal stop, one has to start braking as soon as (or perhaps even before) one has reached line speed coming out of the (n-1)th normal stop. $\endgroup$ Feb 15, 2023 at 12:55

2 Answers 2

3
$\begingroup$

It would be helpful to cite the claim as you are possibly misinterpreting it. Trains absolutely have braking systems which is how they stop at "normal" stops. They take a long time to stop however so unplanned stops are problematic. This is why there are so many train crossing collisions. Cars get in the way and it can take miles to stop a long train. In the olden days trains had a caboose to do braking. Now each rail car has its own brakes. Here is a helpful Wikipedia article. To my knowledge conventional freight trains to not rely on external braking mechanisms.

$\endgroup$
1
$\begingroup$

Modern trains have braking on each carriage or wagon, but this is normally air-actuated, and on a long train, there is a very significant delay for the air signal to propagate down the train, and the valve hardware to respond to that signal. So if the driver suddenly makes a full brake application on a long freight train, the first few wagons near the locomotive will have their brakes locked on, while those at the back of the train are not braking at all.

So the locomotive, and the first few wagons near it, will be pushed along by the rest of the train, and since the wheel-rail friction is low, the wheels will probably lock up and skate along the rail, causing wheel 'flats'. Also the inter-wagon forces caused by the sudden bunching at the back of the train causes problems, maybe resulting in derailment.

The bottom line is that full emergency braking on a loaded freight train is really tricky, despite each wagon having its own brake system.

$\endgroup$
1
  • $\begingroup$ braking on each carriage or wagon, but this is normally air-actuated ... actuated by loss of air pressure $\endgroup$
    – jsotola
    Feb 15, 2023 at 16:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.