Eight of the most congested major roads in Melbourne’s western suburbs are being widened to cope with more traffic and several bridges will be strengthened to handle heavier trucks, as part of a $1.8 billion state government contract.

The Andrews government has entered into a series of 20-year public-private partnerships, valued at $4 billion, to improve and maintain hundreds of kilometres of Melbourne’s arterial road network in the city’s west, north and south-east.

It is the first time an Australian government has used a public-private partnership to complete suburban arterial roadworks.

Private consortiums will pay the upfront costs, for which they will receive quarterly payments from the state over a 20-year period.