San Francisco has placed a firm order for 175 new light rail vehicles for the city’s Muni transit system.

The $648 million order includes an option for a further 85 cars, making it Siemens’ biggest-ever light rail contract in the US.

It is the second high-profile train order for Siemens’ Sacramento factory in as many weeks.

Earlier this month, Siemens won the contract to build two dual-mode locomotives and four passenger cars for the Miami-West Palm Beach section of the planned north-south All Aboard Florida corridor.

San Francisco’s new modern trams, which will start to be delivered by the end of 2016, will be based on the S200 vehicles being supplied to Calgary.

San Francisco mayor Edwin Lee said: “Today, we are truly moving Muni forward.

“By expanding San Francisco’s light rail fleet, these new Siemens vehicles will make our city’s public transportation system more reliable, easier to maintain, and ready to meet the demands of a growing city.

“In addition, these new vehicles will be built right here in California, bringing jobs to our regional workforce.”