Why exactly did they close the south coast line anyway? I heard rumors from somewhere that it was done because there was a relationship between the local trucking company and a senior government minister and it was basically corruption (i.e. the trucking company didn't like the fact that the railway was cheaper/better and used their relationship with the government to get it shut down) but I dont know for sure if that's what really happened or not.
Re the trucking company myth; see my material a few posts earlier and I will repost some here to save you searching for it... The linked page (2MB size) https://drive.google.com/file/d/0ByB-ppGeDyvwcDgwUWFTRjBFQU0/view
has the source name and date on the paper itself. If what local member of parliament at the time, Cecil Charles Carey MLA, says in the paper is true, then his transport company had fewer profits from the route after the rail closure. The 700 tons a week of general rail freight is also an interesting amount as it would only amount to one reasonable train payload a day perhaps. Also notice the article mentions the removal of road tax.
John Knowles has some factual discussion on this general topic. http://freespace.virgin.net/johnk.pb15/southport.html
Another of the closure myths blames Joh although the spreaders of that myths are not smart enough to realise he was not the premier at that time. The premier was Sir George Francis Reuben (Frank) Nicklin (1895-1978), whose grandmother was Jane Nicklin, nee Lahey. Her family were famous for the Canungra Tramway and sawmill. The Laheys also supplied the timber for the Tweed Heads station.
In short, once the highway bridges were opened c1930 over the Logan and Coomera rivers and the Jubilee Bridge over the Nerang River at Southport was opened in 1925, the railway was doomed. The road bridges over the Tallebudgera and Currumbin Creeks in 1926 plus the earlier road bridges allowed people direct access to the tourist resorts. The Jubilee Bridge also allowed buses and trucks direct from Brisbane, without transhipping at Southport, into the tourist areas instead of using Myers Ferry over the Nerang River into what is now Surfers Paradise.
The closure was also because the population purchased cars like the FJ Holden and the Falcon and therefore could load their car boot at home with their holiday gear and drive direct to their holiday instead of loading their gear onto public transport at one end and then off the train and across the streets to the beach or holiday flats or motel. See the car adds on the linked newspaper. The train was lucky it lasted that long.