A subway carriage for Boston's orange line is seen at an assembly factory of CRRC Changchun Railway Vehicles in Changchun, capital of northeast China's Jilin Province, Oct. 31, 2017. The first China-made subway cars tailored for Boston's orange line rolled off the production line on Oct. 16 in Changchun. The subway cars, which will be delivered to the United States in December, are among a 284-carriage order signed by CRRC Changchun Railway Vehicles and Massachusetts Bay Transportation Authority (MBTA) in December 2014. (Xinhua/Zhang Nan)

Workers work in a subway carriage for Boston's orange line at an assembly factory of CRRC Changchun Railway Vehicles in Changchun, capital of northeast China's Jilin Province, Oct. 31, 2017. The first China-made subway cars tailored for Boston's orange line rolled off the production line on Oct. 16 in Changchun. The subway cars, which will be delivered to the United States in December, are among a 284-carriage order signed by CRRC Changchun Railway Vehicles and Massachusetts Bay Transportation Authority (MBTA) in December 2014. (Xinhua/Zhang Nan)

A worker installs the folding seats on a subway carriage for Boston's orange line at an assembly factory of CRRC Changchun Railway Vehicles in Changchun, capital of northeast China's Jilin Province, Oct. 31, 2017. The first China-made subway cars tailored for Boston's orange line rolled off the production line on Oct. 16 in Changchun. The subway cars, which will be delivered to the United States in December, are among a 284-carriage order signed by CRRC Changchun Railway Vehicles and Massachusetts Bay Transportation Authority (MBTA) in December 2014. (Xinhua/Zhang Nan)

A worker arranges a folding wheelchair on a subway carriage for Boston's orange line at an assembly factory of CRRC Changchun Railway Vehicles in Changchun, capital of northeast China's Jilin Province, Oct. 31, 2017. The first China-made subway cars tailored for Boston's orange line rolled off the production line on Oct. 16 in Changchun. The subway cars, which will be delivered to the United States in December, are among a 284-carriage order signed by CRRC Changchun Railway Vehicles and Massachusetts Bay Transportation Authority (MBTA) in December 2014. (Xinhua/Zhang Nan)