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Reading Topic #9151
I live in northeast Minneapolis near the BNSF line south of the Northtown yard. Over the last few months I have seen loaded coal trains with an unmanned helper (a DPU?) at the rear, something I never saw before this summer. Is this really new to this area? Why is it done? I do not think there are any steep grades around here. Does it allow for longer trains?Larry
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Hi Larry,
Two CW44AC locomotives are able to produce 360,000 pounds of starting tractive effort (pull force). Three of them will be able to generate 540,000 pounds at full throttle. Even the best couplers can only handle 500,000 pounds of strain, and that only if it has no shock (jerking) component. Now if you put two AC locomotives on the point and another in the back, you can now use the 540,000 pounds of force and not break couplers.
In addition, this configuration can help very long heavy trains avoid straightening out the curve. If you put a loop in a string and pull on one end, it will become straight as it moves in the direction of pull. Now if you take 115 train cars and pull on one end the same thing trys to happen, and can damage track or derail the train. By adding a correct force on the rear, this effect is lessened. Too much force is worse than none, so DPU control has become more sophisticated, with newest locomotive models having more ability to deliver just the correct force.
Hope this helps,
Bob
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