Roads need to be resurfaced constantly and rebuilt every 30 years or so. You will never finish paying off a road.

@alcoholicorn Yeah, that's not how it tends to work in Australia.

What happens is a state government puts up a good chunk of time construction costs (as much as half in some cases), plus public land.

In some cases, the freeway already exists, but the state government wants one more lane built, because it thinks that will ease congestion (as happened with sections of the Tullamarine and Monash Freeways in Melbourne).

It gets handed off to Transurban, who builds it under a long-term operating agreement (30 years is common).

In some cases, the agreements have clauses saying railways that compete with the toll road can't be built.

As the end of the lease approaches, Transurban offers to build one more lane — in exchange for extending the agreement.

People won't stop driving entirely. Some are legitimately afraid of rain, sun, wind, snow, etc . Placing the toll booths every 100m would go a long way to reducing traffic and reducing dangerous vehicle speeds.