Drivers will have to wait a little longer to find out if NSW Labor's marquee election commitment to cap tolls will apply to them.
From next year, about one in 10 drivers are expected to start sharing in more than $560 million in toll refunds when a $60 weekly toll cap takes effect.
The scheme was a key election pledge aimed at winning Labor seats in western Sydney, where the bulk of the city's tollways are based.
Savings have been estimated based on toll account owners.
But Roads Minister John Graham on Thursday declined to state how exactly the cap would be applied.
That included whether two relatives driving separate vehicles from the same household account would be covered under one $60 cap.
"We will make clear how drivers can register and all these arrangements closer to (January 1)," he told a budget estimates hearing.
"Of course, it's complex delivering this toll relief."
Mr Graham said the government had been up front that the scheme needed careful administration and auditing.
Bureaucrats have been tasked with determining how people could game the system, targeted at private drivers.
A government source floated the use of a "fair use" condition to ensure professional rideshare drivers and people with dozens of vehicles on a single account could not access the relief.
Before the election, the parliamentary budget office priced the scheme at $145 million over two years, assuming it would apply to 51,000 drivers.
But Transport for NSW forecasts delivered after the election indicated it would instead cost three times that and apply to 14 times more drivers.
Opposition transport spokeswoman Natalie Ward criticised Mr Graham for failing to guarantee every driver would be eligible for the toll cap.
"Labor blew the budget on this policy, and now they are walking back their promise," she said.
"It is a simple question: will every driver benefit from the scheme or is this another broken promise from Labor?"
Under the coalition, a quarterly toll rebate applied for people spending more than $375 a year.
Labor will also incentivise heavy vehicles to use the M5 East and M8 tunnels after rising tolls led to more trucks on residential roads.
Trucks will receive a rebate for one-third of their trip travelled on the M5 East and M8, costing $54 million over a two-year trial.
The trial is expected to be succeeded by a new tolling regime in Sydney based on the results of an ongoing independent review led by Allan Fels and David Cousins.
