If the engineer of a freight train is forced to go to emergency braking, do the wheels of the locomotives and/or the cars lock up?
If the wheels lock-up, what happens to them, and what happens to the rail?
Basically, yes, they could…but not all at once. The engine brake is independent of the train brake (but I believe can be set through the train brakes or added to train brakes) and the brakes apply from head end to hind end. Thus, the head cars can be locked while the hind cars are still free…how many and how much of the train depends on full application and length of train…Locking of brakes is what causes flat spots or flat wheels (also caused by a brake that does not release. I am sure you are going to get some much more detailed and even complicated (and correct) answers, but in a nutshell this is an answer.
Several years ago, my suburban train went into emergency braking about a half-mile or so prior to my stop. I was already in the vestibule and recalled hearing the “WHAM” of the trainline but no wheels locking.
A lot is going to depend on the weight of the car and/or whether it’s loaded or empty.
Not to mention a host of other factors (wet rail, ice, etc).
A sliding wheel isn’t going to do anywhere near the damage to the rail that the rail is going to do the the wheel.
A suburban train usually will not lock up, unless there is damp rail, or worse, leaves on the tracks. The Metra suburban trains’ locomotives have a “blended brake” feature that automatically bails off the engine brakes in favor of the dynamics.
Back in the old days when cast iron brake shoes were used on passenger trains (at least they were on the CNW trains), locking the wheels was a distinct possibility; of course, the trade off was extremely aggressive braking on dry rail.
On freight trains, the main danger of emergency applications is there is bad weight distribution in the train (heavy loads behind empties). The empty cars will stop faster than the loads, and if the train blocking is wrong, the loads will “run in” towards the empties, the result being a possible derailment. If the engineer does not bail off the locomotive brakes, the effect will only be worse. (This scenario does not apply if the slack on the train is completely bunched)
Regarding the rail: I’ll confirm what tree68 said.
The air brake system is specifically designed NOT to lock up the wheels during emergency brake applications. Virtually all locomotives with dynamic brakes have an interlock that kicks the DB off in case of emegrency application. Loco air brakes can slide wheels, particularly on bad rail, so engineers try to manage the independent air brakes to avoid sliding wheels to avoid flat spots AND becuase a heavy brake on a rolling wheel will stop sooner than a sliding wheel.
Most flat spots on cars are generally attributed to handbrakes being left applied.
Mac
There are actuaally three differnet brakes on a train as memtioned in several of the earlier posts. There are the engine brakes which will lock up the locmotive wheels, the dynamic brakes electric brakes) and train (air line brakes). Each work independently of each other, except that the dynamic brakes work down to a certain speed and then basically shut off (have no effect on the slowing of the train)…
Many locomotives(for example all CPR AC motored locomotives, all SD60s, and Soo Line SD40-2s) are equipped with the Dynamic Brake Holding feature which will not release the Dynamic Brakes in an Emergency or Penalty Brake application.
Most if not all UP dynamic brake equipped engines also have this feature.
They do have a Dynamic Brake Interlock that is supposed to keep the engine (Independent) brake from applying during dynamic braking when a train (Automatic) brake application is made.
Jeff
Thats Canadian law, All dynamic brake equipped locomotives should have a DB holding feature