The MBTA plans to start running three-car trains on the D Line on Monday in an effort to ease rush-hour crowding, according to General Manager Richard Davey.

Davey said the agency plans to assess the usefulness of the longer trains during the D Line trial and could eventually offer three-car trains on the B Line. He said the MBTA hasn't used the longer trains on the Green Line, which includes both the B and D branches, since 2005.

Davey said the idea for the trial came out of a hisrecent appearance at Reservoir Station, where he talked with commuters and solicited their complaints about the D Line.

"The goal is to provide more space and make our customers' commute a bit more comfortable by increasing capacity on the train," he said in an email to Brookline Patch.

To start the trial, one three-car train will make two roundtrips on the line each morning and evening. The longer train is expected to leave Riverside Station for its maiden voyage at 7 a.m. on Monday.