[1] In September 2008, CapMetro evaluated the need for rail service to alleviate pressure from congestion downtown to Colony Park, with a potential extension to Elgin.

In May 2018, the Travis County Commissioners Court voted 3–2 to move forward with a viability study of the Green Line.

[2] The project's National Environmental Policy Act review is expected to begin in 2028, with revenue service possibly starting in 2033.

A potential future extension beyond Colony Park would feature new stations at Wildhorse, Manor, and Elgin.

[4] The Green Line will be built from Downtown to Colony Park first, with the extension to Elgin considered at a later time.