Acceleration with enhanced load shed (Freight) or AC Coach Count (Dynamo Friction increases with add-in AC ICF/Hybrid Coach)!!
The route where consistent Brake cant b avoided (Stoppage/Congestion) & Freight/Train has to keep pace to avoid OT, acceleration matters whch Twin makes (After reaching threshold, second Alco remain in sleep mode)!!
Freight required Twin to make most out whn gt clearance..smetimes just to cover next station ASAP!!