The two councils responsible for the Aberdeen bypass will not have to pay more than £75m each, Transport Minister Keith Brown has said.
He said Aberdeen and Aberdeenshire councils would have the amount they pay towards the total £745m cost of the bypass, and A90 upgrade between Balmedie and Tipperty, capped.
It means the Scottish government will pay 81% and the councils 9.5% each.
The 28-mile bypass is expected to be completed in 2018.
The Aberdeen Western Peripheral Route (AWPR) was given the green light by Scottish ministers in 2009 but it has been delayed by legal action. Work is expected to begin in 2014.
Mr Brown made the funding announcement as he unveiled the shortlist of bidders for the contract.
Four consortia will compete: Granite City, North East Roads Partnership, Scotia Roads Group and Connect Roads.
Mr Brown said: "The benefits of the AWPR and Balmedie are clear, with the scheme expected to deliver 14,200 jobs in the north east and boosting the economy to the tune of £6bn over the next 30 years.
"After years of delay, we should not underplay the need to ensure the pace in delivering this vital project continues."
The A90 scheme will see the busy stretch between Balmedie and Tipperty in Aberdeenshire become a dual carriageway.
It will provide continuous dual carriageway between Aberdeen and Ellon, aimed at improved safety and faster journey times.