The bank also committed a 300,000-dollar grant to prepare a long-term land use and development plan along the 128-kilometre (79.
4-mile) highway.
"Traffic volume between the southern region and Colombo has increased significantly since the project was first approved, and it remains one of the Government's priorities," said ADB environment specialist Dewi Utami.
"The project will greatly reduce travel time and promote easier movement to and from the southern areas to Colombo, which should increase economic activity."
Poor transport links with other parts of the country, in particular with Colombo and the economically dominant western region, have constrained economic development in the south, the bank said.
The Japan Bank for International Cooperation, the