While bus routes and bus lanes can be chopped and changed over time, trains can beat traffic congestion and most major lines will remain in place.
Moving rail links is phenomenally difficult and cost prohibitive.
Sydney, a little like my home city of Sheffield in England, is a conurbation which once had an extensive tram system.
From 1879 to 1961 the Sydney tramway network was one of the largest in the world before its closure, ironically in part due to overcrowding.
Today it is the street traffic which is becoming overcrowded, and light rail is considered to be one of the solutions.
And here's where the latest line extension will run, opening up the south eastern suburbs to city access:
"A central element of delivering Sydney’s Light Rail Future is the CBD and South East Light Rail project (CSELR).
This new light rail line will extend from Circular Quay along George Street to Central Station, through Surry Hills to Moore Park, then to Kensington and Kingsford via Anzac Parade and Randwick via Alison Road and High Street."
Population growth pressures