The level of overcrowding on Melbourne's trains has jumped significantly this year, new data shows, with almost one in two peak-hour commuters on the city's worst affected lines forced to squeeze into overcrowded trains.

Overcrowding on trams has also risen this year, with the most densely packed services again found on routes used by the city's smallest trams.

Public Transport Users Association president Tony Morton said the train network was again showing signs of strain. Credit:Simon O'Dwyer

On Metro's train network, peak-hour load breaches were most severe on the Dandenong and Werribee lines that service booming outer suburbs. Significant overcrowding was also recorded on the Craigieburn and Sandringham lines.

In all, Public Transport Victoria counted 18 "rolling hour" breaches - meaning passenger demand exceeded capacity in that hour - in its May 2014 load standards survey, up from 11 in May 2013. The survey was conducted from May 5-29 at three city cordon stations: North Melbourne, Jolimont and Richmond.