Although the names of bidders will only be confirmed when the technical bids are opened on July 3, bidders are understood to include Transport for London (TfL), Keolis, France, and Corporación América, Argentina; Paris Transport Authority (RATP) and Alstom; German Rail (DB); Bombardier; and Siemens.
Economic offers will be opened at the end of August, with a view to awarding the contract in October.
The metro comprises six lines totalling 55km plus a 7.4km pre-metro LRT line. Ridership has grown from 900,000 passengers per day in 2013 to 1.2 million in 2017. In addition, 401 new metro cars have been introduced since 2013, while average weekday headways have fallen from 4.06 minutes to 3.14 minutes.