i totally agree with siddharth , when railways want to earn more revenue by chargin Rs 20/- extra, they make it into superfast and increase moving speed above 55 kmph. thats why trains like Dakshin Express, GT Express, North East Express, Ashram Express, Chennai-Howrah Mail, Howrah-CSTM Mail(nagpur), Kolkata Mail(ald) etc etc to name a few ... lot more are there