demand of WAP-7 is not justified, as this train speed is not in excess of 130kmph. as the top speed is less or equal to 130kmph, then it can be achieved by WAP-4 also. also number of coaches is only 10 whereas in Coalfield express number of coaches is around 22-23. also coalfield speed is very good, coalfield express entire journey is in high speed corridor. hence WAP-7 is justified because it need quick acceleration(as number of stoppages are more) and also number of coaches are high.
whereas after DHN, Shatabdi average speed is around 50, so WAP-4 is enough.