In 1989 the Gungahlin External Transport Study (GETS) was undertaken. It was meant to assess future transport needs for Gungahlin residents - before Gungahlin had even been mapped out or a single new home constructed. These articles are from the Canberra Times and can be found online at Trove.
ACT Light Rail have a copy of the resulting report, but it is in hard copy and yet to be scanned.
Following the GETS study Gungahlin ended up with inadequate roads and finally in 2012 a light rail proposal. This 1991 CT article is quite prescient.