I've ridden plenty of peak period double deckers in Sydney over the decades
Matthew to see how they work.

The reason that a polycentric Sydney won't become a car-oriented city is
because the population is around 5 million headed in the direction of 8
million and if everybody tries to drive at that sort of level, the sheer
magnitude of congestion de-incentivates them. We already see people being
interviewed on their metro experience saying how their car journey had
become so long timewise that they were changing to the train to radically
cut the time of their commute.

On top of this, it's becoming extremely difficult to park. The planning
system has been moving against providing parking space in developments for
years while at the same time, lots of parking space is being provided at
railway stations and transit interchanges. While it may not entirely wipe
driving altogether, it contrains it to the nearest transit interchange. The
next step is to get the bus system working so well, as it does in Perth,
that more people will take the PT journey starting from their homes.
Channel 7 in Perth did an excellent couple of surveys in different years a
while back with a comparison of a direct car journey from home to the Perth
CBD with a bus from home, changing to train journey and the door to door
bus/train journey was several minutes faster than the car journey.

Combine a frequent, efficient bus journey with a frequent, *fast* train
journey and you have the formula.

Tony P