Rising costs for the Yanchep and Thornlie to Cockburn rail lines, and two new investments, have helped lift the state government's bill for 18 Metronet projects to $9.1 billion.

Rising costs for the Yanchep and Thornlie to Cockburn rail lines, and two new investments, have helped lift the state government's bill for 18 Metronet projects to $9.1 billion.