With new trains for the Red and Orange lines on the way, the Massachusetts Bay Transportation Authority is eyeing its next shiny new cars: a fleet of Green Line trolleys that could vastly increase capacity on the nation’s oldest subway line.

The MBTA is considering a number of improvements that would overcome longstanding obstacles to using bigger cars on the Green Line, such as short loading platforms and tight turns at some locations. If the right improvements are made, the MBTA would be able to buy 165 or more trolleys over the next decade that are about 40 feet longer and hold twice as many riders as those in today’s fleet.


It wouldn’t come cheaply: All together, the trolleys and the infrastructure work they require would cost at least $3.5 billion, the T estimates. But with the potential to double the capacity on a line that carries about 200,000 people a day, the project would be worth the price, said the MBTA’s deputy general manager, Jeff Gonneville.