Trains at night can only be feasible in long distance rail
systems. Throughout the World, there are really few train systems
which run trains overnight with regualr frequency, as in trains
come in 20-30 min or any other fixed frequency. Even Japanese or
European systems reserve the night track usage to sleeper trains
and freight trains.
Track maintenance is one thing, the usability is also another...
Repair works can be done while train is running, just that the
responsibility of the train operators must be there. Working on the
tracks is dangerous business.