The Massachusetts Bay Transportation Authority commuter rail alone has more than 130,000 boardings every day, with another half-million or so on the subway itself. The trains from suburban Boston into the city and back out are as important to the operation of that large metropolitan area as the Maine Turnpike and Interstate 95 and all the state routes are to central and southern Maine.

The assumption among many Mainers has been that rail travel could never usurp car travel, or even augment it to any real degree, because of the smaller population, the lower building density, and perhaps the absence of parking and traffic issues that drive people to public transit.

The Maine Rail Transit Coalition thinks otherwise. The group will have a chance to make the case in the coming months, as the debate begins about the future of a 30-mile rail line from Portland to Auburn where freight service soon will be discontinued.

The coalition’s plan for a passenger rail along the corridor would require significant public investment — local, state and federal — and help from private investors. But rail service between Maine’s two largest population centers could increase property values and spur business development. It could take cars off the road, lessening the environmental impact of Maine’s transportation system and lowering the cost of maintaining roads. And it could provide a starting point for a larger-scale public transit system that benefits much of the state.

But first, a lot of questions must be answered. The obvious question is whether a rail system can work given the demographic realities in Maine. The coalition says it can, and has elsewhere in areas much like Maine, which itself has seen ridership for the Portland-Brunswick Downeaster train exceed expectations in its first year.

The population of the Portland-Auburn corridor is around 250,000. The coalition points out the rail corridor from Beaverton to Wilsonville, Ore., has a population of 440,000. The commuter rail in Santa Fe, N.M., has 396,000 people.

Both of those commuter lines have found fans and experienced ridership growth, but they also have been criticized. Some of that has been based on mismanagement and a failure to meet stated goals. Most of the criticism, however, is centered on cost. Part of that is cultural, as taxpayers see money spent on rail service as a subsidy, while they have no problem spending billions of dollars on road maintenance.

Tony Donovan, a founder of the Maine Rail Transit Coalition, points out that maintaining roads costs around $1 million per lane per mile, and work must be completed every 10-12 years. Railroads also cost about the $1 million per mile to maintain, but only every 40-50 years. That could save a lot of money, and a lot of wear and tear on the heavily traveled roads between Portland and the Lewiston-Auburn area, as long as people can be convinced to ride the rails.

To entice riders, the service would start on India Street, near downtown Portland, and at the Port of Portland, where cruise ships dock, and include stops in Falmouth along Route 1, Yarmouth Village, Pineland in New Gloucester, and at the Auburn airport. Donovan said additional amenities, including transportation features such as buses, rental bikes and pedestrian opportunities, would build up at the stops, with the communities’ input. The line eventually could extend to Montreal.

The coalition is lining up private investors for the train platforms, stations and equipment, for a total of $20 million. A $27 million state transportation bond would leverage the federal funds needed for the remainder of the estimated $138 million project. Operations could be paid for in part by assessments on property value increases that occur because of the nearby rail service. The Department of Transportation is working on a report detailing funding mechanisms for design and engineering work.

If it comes to it, the transportation bond would have to be approved at the statewide ballot. The bond should stand on its own, so Maine can give the project a clear up-or-down vote.

Until then, Mainers should press for more information about how the rail service would enhance the communities along its path, and how the supposed benefits to energy efficiency and transportation costs would be measured and held in account.