Kerala is the longest electric-hauled train on Indian Railways i.e. run with the same electric loco (usually a WAP4) for its entire journey of 3037 KM. It has eighteen 1 or 2 or 3 minute halts, which it has to strictly adhere, otherwise whole schedule is disturbed and the train becomes late. So the P4 needs to be extremely robust and fit, to carry this 24 coach very tight schedule train.