While the MBTA's draft five-year capital plan does not include funding for subway-like railcars to run along inner-city commuter tracks, Transportation Secretary Stephanie Pollack indicated such service could potentially be added on that five-year timetable.

Diesel multiple units, known as DMUs, run along commuter rail tracks, offering the prospect of more frequent service for areas including Dorchester and Mattapan, served by the Fairmount Line, according to the MBTA, which in the fall of 2014 announced it was going out to bid to purchase 30 DMUs.

"The introduction of DMUs on the Fairmount Line will reduce travel times and offer more options for travelling in and out of downtown Boston," Beverly Scott, then the MBTA general manager, said in an October 2014 statement.

The MBTA announced that in December of that year it would issue a request for proposals for the procurement of 30 diesel multiple units, which transportation experts say provide a more nimble means of transport along rails trafficked by multi-car commuter trains.

In 2014 the MBTA planned complete delivery of diesel multiple units by 2020 with service first offered on the Fairmount Line, which stops at Upham's Corner, and continues out to Readville, an outlying neighborhood of Boston.

"We rescinded that [request for proposals] before proposals were due," MBTA General Manager Frank DePaola said after a meeting Monday.

The draft five-year $14.3 billion capital plan for the MBTA and the rest of the state's transportation system does not include any funding for diesel multiple units, said Pollack, who said she anticipated some public feedback on that.

"We know that that's a thing we're going to hear a lot about in the public process, and we're continuing to look at the feasibility of DMU technology and what a timetable could be," Pollack told the News Service after giving a speech in Everett last week.

Everett Mayor Carlo DeMaria said he would like diesel-multiple-unit service to his city, which is traversed by the commuter rail but lacks a commuter rail station.

DePaola said the MBTA will be "exploring" the use of refurbished equipment to run "small train sets" on the Fairmount Line.

Pollack said she expects to hear from some who want diesel multiple units within the next five years, and indicated that is still on the table.

"That decision will be made down the road," Pollack said. The draft plan focuses on repairs to existing service and modernization of facilities with a smaller emphasis on service expansion.

Rafael Mares, vice president at the Conservation Law Foundation, said diesel multiple units can accelerate and decelerate more quickly than full trains and he would be "thrilled" to see the MBTA use shorter trains on the Fairmount Line to provide more frequent service.

Pollack has previously said transportation overseers would revisit the five-year plan annually.

Details of the projects included in the draft $14.3 billion capital plan will be made available at the Massachusetts Department of Transportation Committee on Capital Programs meeting on Tuesday.