Buenos Aires has ordered an additional 60 300 series trains from Alstom.
The new air-conditioned units will go into service alongside the Alston-built 100 series fleet on Line D between Congreso de Tucumán and Catedral.
Around 340,000 passengers use the line every day.
Alstom is currently building 300 series vehicles, which feature pneumatic suspension and regenerative braking, for line H.
The new Line D units will allow Subte to operate 30 trains an hour on the route at peak times.
