Is the future of the Mattapan line more trolleys, or buses?

A trolley on the Mattapan Ashmont High Speed Trolley Line leaves Ashmont Station.Lane Turner/Globe Staff

The Green Line may not be the final destination for the 24 new trolleys the MBTA is adding to the subway system this year.

Even though nearly all of the new cars have yet to be deployed, transit officials are already considering their second act a decade or so from now: on the Mattapan trolley line, when the 73-year-old cars that currently run on the line may finally reach their end.

Earlier this week, the Massachusetts Bay Transportation Authority unveiled several options for the old-school trolley line that runs between the Ashmont Red Line station and Mattapan. The aging fleet is down to just six trolleys for now, and the T is spending about $8 million to rehabilitate the cars one more time, which should extend their life another eight to 10 years.

Among riders, the future of the old trolleys has been widely debated: Some love their historic feel, others think it’s time to move on.

The agency, though, is already considering what comes next. There doesn’t seem much enthusiasm to keep rehabbing the old cars. At a public meeting Monday, MBTA chief engineer Erik Stoothoff noted the old trolleys are not easily accessible for riders with disabilities and do not work well with modern collision-avoidance technology.

Other options include buying replica versions of the old trolleys, a historic model called a Presidents’ Conference Committee streetcar, or buying brand-new, modern cars.

But since the trolley fleet is quite small those options may prove prohibitively expensive on a per-car basis because the T would not be buying in bulk. The T currently uses four cars at any one time for daily service on the 2.6-mile line.

Another option is paving over the rail line and running buses instead, but Stoothoff noted neighbors and riders are strongly opposed. He also said it would be more expensive to pave over the tracks than to simply improve them for a different type of rail vehicle.

And that other rail vehicle may turn out to be one of the new Green Line trolleys. In December, the T introduced the first of the 24 new trolleys, which it plans to use to supplement the existing fleet and keep service steady once the Green Line extension to Somerville is completed in late 2021.

But the T is also planning to get many more of the new Green Line cars over the next decade. Their arrival could free up some of the first generation of new trolleys to move to the Mattapan line.

“Those vehicles will still be very young at 10 years old,” said Stoothoff, who described the switch as a “very real option for us.”

The T’s top leaders, however, don’t yet seem fully sold on the idea. Joseph Aiello, chairman of the T’s board of directors, noted the new Green Line trains will be more expensive to maintain a decade from now, when they are nearing the midpoint of their useful life.

Meanwhile, Transportation Secretary Stephanie Pollack doesn’t want T officials to so quickly dismiss buses. She said they could prove more reliable than trolleys, which are vulnerable to losing power if their overhead wiring is knocked out of service during nor’easters and other storms.

Given the divergent viewpoints, and the number of public meetings on the Mattapan Line still ahead, the T is not expected to make a final decision in the near future.