Construction work has commenced on the $113m South Bay Rapid project in California.

The project will be jointly carried out by the San Diego Association of Governments, the Metropolitan Transit System and Caltrans.

The two-phase project will involve the construction of a 21-mile bus route that will serve as a link between Otay Mesa Port of Entry and downtown San Diego.

Phase one will include the construction of seven stations, access ramps, arterial transit-only lanes, transit signal improvements, as well as improved customer amenities.

Plans for the final phase will involve the construction of new freeway-level stations, Park & Ride lots and other upgrades to reduce journey time.

The service, anticipated to be operational from 2018, will be operated by San Diego Metropolitan Transit System.