The Don Muang Tollway will be extended by 18 kilometres, connecting the Rangsit-Bang Pa-in section to the M6 motorway to Nakhon Ratchasima, the Highways Department announced on Monday.
The proposed 40-billion-baht extension would also link the elevated tollway to the M5 motorway, and could be open by 2025, department chief Anon Luangboriboon said.
The extension would be divided into two contracts - one for the construction work, worth about 28.1 billion baht, and the other governing maintenance and administrative costs, worth about 11.8 billion baht.
Two public-private partnership (PPP) models were being studied -- net cost and gross -- with an economic internal rate of return set at 13%.
Under the net cost arrangement, the private partner collects toll revenues at a specified minimum rate that covers the project's operating cost. The government is obliged to cover any operational losses, but any profit made by the private partner has to be shared with the government as previously agreed.
With the gross cost model, the state assumes the responsibility of collecting the fares, and a private company will be granted a concession to operate and maintain the facility.
Mr Anon said a market sounding process would be held, where businesses and prospective investors would be invited to give their ideas about the project.
"Their input will be incorporated into the project, the details of which will be wrapped up and forwarded to the Transport Ministry for consideration at the end of this year or by the latest early next year," he said.
After that, the project would be referred to the State Enterprise Policy Office and the PPP Committee, which would decide whether to approve it in principle.
Mr Anon said bids could be called as early as 2021 and the winner announced later in same year. "Construction is expected to begin in 2022," he said. It could be open for use by 2025.