Double-heading
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In railroad terminology, double-heading or double heading meant the use of at least two steam locomotives at the front of a train. Some trains even required triple-heading. This was done when a single locomotive was not sufficient to propel the train. This could be due to uphill grades, excessive train weight, or a combination of the two. Double heading was also used on passenger trains when one locomotive could suffice but would not be fast enough to maintain the schedule.
Double-heading was a risky proposition, requiring careful cooperation between the engine crews. If one engine tried to pull harder than the other, its wheels could slip, which in turn could lead to a number of unpleasant consequences.
The risks of double heading as well as its costs (fuel and maintenance costs for the engines, wages for their crews) led railroads to seek solutions to the problem. Electrification was used in some cases. The Milwaukee Road was able to switch from triple-headed steam locomotives to a single electric locomotive. The costs of running extra steam locomotives were eliminated, and average train speeds increased because it was no longer necessary to attach and detach the locomotives.
With the advent of diesel locomotives, double-heading disappeared. While many trains today operate with multiple locomotives, this is not considered double-heading as they are all controlled by a single crew in the lead locomotive.
