It was a case of two worlds coming together as Sydney showcased the old and the new.

In Sydney's Hills District, rail track began to be laid at Rouse Hill for the $8.3 billion north-west metro rail link, the first stage of Australia's largest public transport project.

And in a nod to the city's rail history, a "Red Rattler" rolled over the Harbour Bridge, marking the 90th anniversary of Sydney's first electric trains. Known as the F1, the restored vintage train included one of the original carriages that crossed the bridge in 1932.

As in bygone years, the building of a rail system is still a point of contention.