Straze wrote: I propose to take the line underground so that eventually it could be extended to Harbour Town at West Beach and allows further extension in the City & to other areas of Adelaide at a later stage.
You don't need the entire line to be underground just to build an underground extension.
The reason why i propose it to be a rapid transit line rather than a light rail line is because i want to prepare Adelaide for the increase in population we may get for years to come if we make the wrong choice now we will later regret it and it will cost alot money to fix it.
That reminds me of when Heathrow Terminal 4 was built. The Underground line to it was built as a loop, with all trains running to T4 before T123. But they took a long time to get from T4 to T123 because the line detoured to the planned location of Terminal 5. But when Terminal 5 was actually built (twenty years later) it was located over a kilometre further W.
We should avoid obvious false economies, but it's equally important to avoid wasting money building unnecessary infrastructure on spec. Also keep in mind that money has an opportunity cost, and in the short term it's not readily available.
I dont think there is nothing wrong with taking tourists underground as providing them with a fast service would attract them.
Any rail service between the City and the airport would attract a good proportion of tourists.
In London there is a dedicated rail service for the airport and its still sustainable.
The airport? London has several! I think the one most comparable to Adelaide Airport* is London City Airport. This is linked to the City by the Docklands Light Railway, which is mostly elevated and has quite closely spaced stations.
* Close to the City, and passenger numbers are slightly lower but growing quickly.
In terms of aircraft types and numbers of flights, Stansted is more similar, but it's a lot further from the City.