I think the cost saving will be realised by not having to expand the road network as quickly if they convince people to use public transport. The cost of land acquisition/resumption along with the improbability of widening some central bottlenecks like Coronation Drive, the SE Arterial and the hell-hole that is Hale Street.

Personally, the $1 commute from the Sunshine Coast has been very good. I occasionally drive in but the Bruce Hwy has been a constant process of widening each section as they barely keep up with the traffic increases.

I think what you will see is a lot more people moving out to residential areas north of Brisbane seeking cheaper housing as they can take advantage of the almost free travel. Especially if they eventually build the Rail/Light Rail through South Caloundra to Maroochydore.