This has been cleared that in indian railways Rajdhani,shatadi exp get highest priority in any route ,and give given shortest travel time between that section.becuase the travellers of this people are aristrocraft and they pay huge amount to travel these train.not for for any urgent matter.
for example where all premium trains in kolkata new delhi routes rajdhani,durantos,yuva having 5,6 halts able to to cover such distance in 17 to 18hr,
while all others non premium trains like poorva express,wb sampark kranti are taking min 24hr with having 5,6 halts thought these trains...
more...

have ability to cover such distance in 21hr or 20hr.Still Indian Railways dont think to comfort journey for maximum common people.
Same like in kolkata New jalpaiguri route.only premium train shatabdi express with three halts making such distance in 8hrs.while darjeeling mail having 4halts many days finds it difficults to cover it in 10hr ,though it can be covered by 9hours too with 5,6 halts too.
When HWH NJP shatabdi exp is able to make it in 8hr with green signal all the way ,then why not others top class trains like haldibari intercity,saraighat exp,darjeeling mail ,padathik express given green signal to make it atleast 9hours?which is possible.
shatabdi average speed 70kmph.cant others trains min 60kmph?
the glory of superfast of darjeeling mail somehow reduced in introduction of speed master shatabdi exp.