Peak-hour commuters on three of Melbourne's most overcrowded railway lines will receive a handful of sorely needed extra services when a new Metro timetable starts in August.

The timetable update will usher in new peak-hour services on the Werribee, Sunbury and Craigieburn lines.

Commuters pour out of Flinders Street Station. Credit:Vince Caligiuri

Those three lines are each among the worst in Melbourne for peak-hour overcrowding, with multiple trains per day that breach Public Transport Victoria's load standard of 900 passengers per train.

The three lines will each get an extra morning peak service and an extra evening peak service on weekdays, adding 30 new services to the timetable.