Transport ministry secretary Wasantha Karannagoda said the ADB had promised 500 million dollars over the next three years for the first phase of the project.
"Land acquisition studies and detailed designs have been done and we hope to start the civil works from next year," he told a news conference.
"The expressway will reduce travel time between Colombo and Kandy to around 45-50 minutes with vehicle speeds of 100-110 kilometres an hour.
It will be a four-lane highway with provision to expand to six lanes.
"This will be a big relief to commuters, enabling them to save time and fuel, and reduce vehicle maintenance costs.
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Travel between Colombo and Kandy now takes about three hours and there is congestion on the existing road.
The planned expressway will be an elevated highway, built on viaducts or concrete pillars in order to reduce land acquisition and avoid difficulties caused by the danger of floods, Karannagoda said.
The first phase from Kadawata, north of Colombo, to A