Champaran HumSafar Express : इन अजनबी सी राहों में, जो तू मेरा हमसफ़र हो जाये, बीत जाए पल भर में ये वक़्त, और हसीन सफ़र हो जाये. - Piyush Singh

Few points why KK is hauled by twin locos...
1.The most common reason is 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.
2.Double-heading is also used on passenger trains when one locomotive could suffice but would not be fast enough to maintain the schedule.
3.More...
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rarely, double-heading is used 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.