After completion of the Khulna-Dhaka Rail link via Padma Bridge, the trip from Khulna to Dhaka will take 3 hrs. using currently available equipment instead of the current 8-10 hrs.
A rail trip from Kolkata to Dhaka will also be possible in 4 hrs. Which means one would be able to go to Kolkata from Dhaka and come back in the same day - especially if faster speed rail equipment is introduced.