Hey Louis,
In Queensland, this is the go:
www.qld.gov.au/transport/vehicle-safety/transporting-loads/how-to-transport-loads... so if it's not hanging out, if it's not impeding your vision, and if it's not likely to maim anyone in an accident, you are right to go.
I imagine it's similar in NSW but gave up looking after I realised Gardening Australia was on.

I had no idea bromeliads came in so many kinds.
Anyway... I say go for it.
Greeney