Quick answer
Longer trains can move more freight with fewer train movements, but length also makes train handling, braking, in-train forces and blocked crossings more complex.
Efficiency and capacity
Combining freight into longer trains can improve use of crews, locomotives and track capacity. Modern distributed-power technology also helps railroads manage longer, heavier trains.
Long trains are harder to handle
The Federal Railroad Administration has highlighted that in-train forces become stronger and more complex as train length increases. Train makeup, braking and communications therefore matter greatly.
Why DPUs are common on long trains
Mid-train or rear locomotives spread traction and braking forces instead of putting everything at the head end, which can improve handling of a properly configured long train.
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