The photo shows what happens when a train with multiple engines has the brakes applied, but an engine does not get a signal to shut down.
Actually, the whole train brakes. Every wagon has brakes, not just the
locomotives. What is interesting is that somehow the signal bypassed
the dummy locomotives (only the first one usually has people operating
it, the rest are controlled by remote from that first engine) and got to
the wagons, or the dummies were at the rear of the train and the signal
broke somewhere in the middle. Also consider that static friction is
stronger than kinetic, so as the first engine slowed and stopped, the
following engines could have started slipping and never regained
traction.
There's more discussion at
two Reddit posts, and more pix
here.
Here's a couple of follow-up comments from the Reddit thread in response to the one you quoted:
ReplyDeleteFrom Rounding_Error: It "bypassed" the second and third locomotives because the air brakes were applied on the entire train. This kept it the entire train from moving, but was not clamped tight enough on the powered wheels to keep them from spinning. The traction motors in diesel locomotives have a lot of torque at low speed. Suppose this was a 100 car train with three six axle locomotives, that would be 818 wheels with the brakes applied vs 12 that are powered. Even if the brakes were lightly applied on the entire train, this would likely happen.
From Not_Mine: Actually there are 2 braking systems on American trains.
The automatic brakes will apply the brakes on the whole train, including the locomotives. There are also independent brakes that only apply brakes on locomotives. When the automatic brakes are applied, the independent brakes can be actuated (released) without affecting the cars.
One of the reasons for two systems is so the train can start pulling the train while the brake lines are being charged. This prevents the cars in the rear of a long train from having the coupler knuckles from breaking if the front of the train is moving at a rapid pace and the rear of the train is still stopped.
There could be may other reasons for this, but I never had enough seniority to become an engineer.
(Mel V. back in) So it sounds like there's more to it than the 'signal breaking' and skipping the dummy engines, there's a couple of systems involved here. Cool stuff.
Very interesting!
ReplyDeleteWhat happens when the train goes over that part of the track...?
ReplyDeleteIt might derail, but it would probably make a huge bump and not derail.
DeleteI'm not sure it would even cause a bump. The depression would affect only one pair of wheels at a time, but there are multiple pairs of wheels supporting any given boxcar. I bet the one going over the depression would sag for a moment, but the car as a whole wouldn't notice the dip.
DeleteAt about 30 mph the suspension will soak it up but the rail will break shortly
ReplyDelete