प्रयागराज एक्सप्रेस - जो भी हो तुम खुदा की कसम; लाजवाब हो

i travelled by this train on 31 dec 2011 from umb to juc. train was late by 2hrs 30 min. it arrived at 7:30pm. but when train arrived at umb i was very surprised to see that it was hauled by tkd wdm 3a instead of gzb wap4/7. i don't understand that why it was given with a diesel locomotive on fully electrified route.

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