The massive suburban loop project at the centre of the Andrews government’s election win will not connect workers to jobs, a Grattan Institute analysis reveals.

The $50 billion suburban rail loop, connecting nearly every metropolitan train line in a ring around the city, would not achieve the key aim due to the low number of jobs in Melbourne’s middle suburbs, Grattan's transport program director Marion Terrill says.

Premier Daniel Andrews and Public Transport Minister Jacinta Allan discuss the suburban loop in Box Hill in August. Credit:Joe Armao

The 90-kilometre, mostly underground rail line would connect existing train lines with universities, hospitals, shopping centres and the proposed airport train station.

The government hopes this will see Melbourne become a 'polycentric city', meaning that housing and jobs would cluster in locations outside of the CBD.