This is where the public transport equation enters the mix. First, the tolls on the roads could fund dramatically reduced public transport fees — maybe even negative ones (where you effectively get paid to use public transport). As noted by The Sunday Age, that would reduce congestion problems on roads.
Second, if e-tags could be used to charge cards, why couldn't they be used to credit public transport users? Get on a tram, swipe your card and you get a credit. The credit may be towards your road account so commuters would face a double incentive not to use roads, or at least use them at the right times.
...The result would be a technological means of pricing externalities and an improved environment. So I don't think The Age's idea is that radical. It is a blindingly sensible step towards good management of the transport system.https://www.theage.com.au/business/road-use-charge-would-force-more-to-public-transport-20060307-ge1vv5.html
The mystery is why so-called environmentally conscious governments do not consider the idea.