The JICA said about 38 percent of the tolls from the expressway and the highest volume of vehicle movement is seen at Kottawa.
The volumes are expected to rise with the completion of the first section of the Outer Circular Expressway in 2013.
The toll plaza was financed by JICA. The agency has also loaned 36,269 million Yen (about Rs50bn) to finance the 66 kilometres of the 95 kilometre expressway.
JICA has given technical assistance as grants, training over 300 toll collection and traffic management staff.
"A new grant project to set up ‘Intelligent Transport System’ (ITS) facilities on the Southern expressway to provide advance traffic and road condition information to expressway users is currently in discussion between JICA and government authorities," the agency said.
President Mahinda Rajapaks and Japan's ambassador to Sri Lanka Nobuhito Hobo will is to commission the plaza and a service area at Welipanna on Wednesday.JICA will also hand-over 20,000 ‘reflective warning triangles’ for distribution free of charge to the users of the Southern Expressway. The warning triangles can be used to warn other drivers in case of a breakdown or other emergency situation.