MEXICO CITY (Reuters ) – Mexico City's government said Thursday it awarded a $1.7 billion contract to build a new subway line to a consortium led by the country's top builder, ICA.

France's Alstom and a company owned by Mexican billionaire Carlos Slim, one of the world's richest men, are also part of the winning group.

The new 24 kilometer line will run through the south of the capital as authorities battle to improve transportation in the traffic-clogged metropolis of around 20 million people.

“This would be the biggest public construction granted in this administration,” Mexico City Mayor Marcelo Ebrard said.

The new subway line, with 22 stations, is expected to transport nearly half a million people daily.

Construction is due to start next month and should be finished by December 2011.