Having to pay to travel on the F6 extension could take its toll on some motorists.
While the government has not committed to building the extension, Roads Minister Melinda Pavey has said a project of that size would come with some sort of toll attached.
A cabinet document suggested the cost to travel the full length of the extension could be as much as $10.
That would mean Illawarra motorists already travelling on Sydney’s other toll roads would need to find more money for their daily commute.
Or, according to University of Sydney Professor David Hensher, they might decide the extra cost isn’t worth it.
Prof Hensher has put forward the concept of "toll saturation”, where people reach the maximum they will pay.
“Because Sydney has more toll road kilometres than any other city in the world, as we build more and more tolled links there comes a point where the threshold is such given your budget that you’re no longer prepared to spend any more money on tolls, even though there might be some claimed time savings,” Prof Hensher said.
“In other words you don’t make a time-cost trade off in deciding ‘well here’s the toll, here are the benefits’ without realising there’s a limited amount of money you’re willing to commit to paying tolls.”
Prof Hensher said that once people hit that toll saturation point they will seek out free routes instead.
He said people in the Illawarra driving to Sydney for work would be particularly susceptible to hitting this saturation point if the F6 extension was built.
“It doesn’t mean they won’t opt to use one of the new toll roads as they’re built,” he said.
“They may opt to use that but then opt out of some of the other tolls roads they were using before, depending on where they can see the greatest benefit.”
He suggested time-based tolling – where the cost was dropped for off-peak travel – to encourage traffic to spread out and better use the road network.