Commuters are making millions more trips on the overcrowded Geelong line as customer satisfaction on the state's regional rail service falls to a 10-year low.

Geelong train trips have more than doubled in the past five years, while the number of commuters using new train stations at Wyndham Vale and Tarneit has grown by 20 per cent and 17 per cent, respectively.

The opening of the $3.6 billion Regional Rail Link in 2015 spurred the explosion in commutes, coupled with a housing boom in Melbourne's western suburbs.

Geelong train trips have doubled in five years. Credit:Luis Enrique Ascui

About four million annual trips were made on the Geelong train line five years ago. That skyrocketed to 10 million in 2018, V/Line's 2019/20 annual report shows. This far outpaced the level of growth on every other regional line.