Technical and engineering studies are currently being carried out in preparation for tendering, which should begin by the end of the year.

Prior to the inclusion of the Bosa extension the line would have been 26.5km long with 28 stations and an anticipated pricetag of $US 3.6bn.

Initially, services were due to have commenced in 2016, but the project has been delayed by a government corruption scandal. Construction is now expected to begin in the first quarter of next year and be completed by early 2019 at the latest.