The $US 233.1m project will extend lines E and F 3.7km south from their current terminus at Lincoln, following the I-25 highway corridor to the south side of RidgeGate Parkway in Douglas County.

The extension will be constructed by Balfour Beatty Infrastructure under a $US 140m design-build contract awarded by RTD last year.

Commissioning is scheduled for 2019 and, in addition to lines E and F, the extension will be served by a new R Line linking RidgeGate Parkway with Aurora and an interchange with the recently-opened commuter rail line to Denver International Airport at Peoria