Melbourne's busiest railway lines will be overwhelmed by passenger growth within three or four years, leaving more and more commuters unable to board peak-hour trains, new figures show.

The city's rail capacity crisis is expected to hit hardest on lines in the western and northern suburbs, which are projected to hit bursting point at least seven years before the planned solution - the $11 billion Melbourne Metro rail tunnel - is completed.

The latest projections from Public Transport Victoria predict growth in peak-hour patronage of about 90 per cent on the Werribee/Williamstown lines between this year and 2025, 80 per cent on both the Sunbury and Upfield lines, more than 70 per cent on the South Morang line and more than 60 per cent on the Craigieburn line.