With the T2T to Darlington section they have really missed the bus with one huge opportunity. The Seaford Line could have been Cut and Covered between Emerson and Tonsley to allow the expressway to be built on top creating a "Transport Corridor" when the Seaford (then Noarlunga) Line was relaid. I mentioned this at the time to a DPTI Projects Boffin at the time but was told that it would cost too much. I countered with an observation that there would not be the huge acquisition costs of building along the South Rd position. However, now that we have a Liberal Government in place, this might be a possible goer as an argument between Libs and Labor has been the position of this corridor with the MATS Plan having the corridor "mid block".Cut and cover would be maybe a year of the railway closed (again) - "Skyrail" with the road would probably be the only option... and people would still go crook about the visual impact if the road was above the railway line - look at "Sky-Rail" in Melbourne, I think what actually ended up happening there was a good outcome but people still b*tch relentlessly (maybe they're right?).
Cut and cover is an excellent engineering solution and doesn't resume lots of land unlike Torrens to Torrens - but it means closing the corridor while the structures are built and politically it's a hot potato completely shutting a road.