parking fees via tag

In Australia, many of the road tolls are paid via electronic tag. As the car passes certain points on the motorway, the tag is read and the appropriate dollar amount is taken from an account.

Surely it would be fairly simple for shopping malls and carpark operators to hook into this. So rather than taking a cardboard ticket that can easily be lost or destroyed, the tag is simply read when the car enters and exits the parking facility.

Not all cars have tags, so both systems would have to remain, but for people with electronic tags in their car, it would make things so much easier.