Starting this summer, the Green Line is going to look a little different. The first of 30 new Green Line cars has arrived in Newton for testing, a major step in the process of expanding Massachusetts Bay Transportation Authority service north beyond what will be a relocated Lechmere Station, where it currently ends, to Medford. The new cars will be introduced into the system starting in July, even though the new extension won’t open for several more years.

The Massachusetts Department of Transportation and the Massachusetts Bay Transportation Authority hosted the first in a series of public meetings to discuss the Green Line Extension Project Wednesday. According...