The MBTA has approved a $310 million purchase involving electric trains and diesel locomotives, drawing questions from transit advocates about how the investment fits with its push toward cleaner commuter rail, MassLive reported.

The agreement brings both types of equipment into the agency’s purchasing plans. While the T describes its efforts as progress toward a cleaner system, advocates are questioning whether the latest acquisition advances that goal, according to MassLive.

The central issue is the diesel portion of a deal that also includes electric equipment. The purchase puts the agency’s current fleet decisions alongside its stated direction for commuter rail, with advocates scrutinizing whether those decisions align.

The supplied MassLive summary does not detail the number of trains involved, how the $310 million is divided between equipment types or the agency’s explanation for purchasing diesel locomotives. It also does not provide a delivery schedule or identify which commuter rail lines would use the equipment.