Double heading

In railroad terminology, double heading refers to the use of two locomotives at the front of a train, each operated separately by its own crew. Triple-heading refers to the use of three locomotives, while multi-heading refers to the use of multiple locomotives.

The practice originated during the era of steam locomotives, but the use of two or more locomotives also remains common with modern diesel and electric locomotives. However, modern locomotives often operate using multiple-unit control, in which all locomotives are controlled by a single driver from the leading cab, rather than by separate crews.

Advantages

Double heading is practised for a number of reasons:

In the UK it was usually to gain traction on steep inclines, twice the amount of driven wheels – twice the amount of grip.

The need for additional motive power when a single locomotive is unable to haul the train due to uphill grades, excessive train weight, or a combination of the two.

Double heading is also used on passenger trains when one locomotive could suffice but would not be fast enough to maintain the schedule.

More rarely, certain companies have used double-heading to guarantee a service when they have been aware of the poor quality of their locomotives, on the understanding that if one engine failed in service, the other would suffice to get the train to its destination.

Double heading is a useful practice on single lines even in the absence of a need for more power, as to double-head a train saves making a separate path for a spare engine; it can be repositioned using the traffic path occupied by the service train.

As double heading has become increasingly uncommon railway companies may advertise specially double-headed services as an attraction to enthusiasts; this occurs regularly but infrequently on the British mainline, whilst the Romney, Hythe & Dymchurch Railway in England advertises an annual day when all of its passenger trains are double-headed all day, both steam and diesel.