The 8.5km line will extend the existing TransPerth Midland line through an 8km twin-bore tunnel beneath the Swan River to reach Perth Airport.

Geotechnical surveys for the tunnels were completed in December and construction is due to begin in mid-2016. Commissioning is scheduled for 2020.

The project will be delivered as a single design-build package and details of the tender will be published on the Western Australia government tenders website.