Public transportation is often seen as something too expensive and too urban for a rural state like Maine, making it a dream that fits only in our long-range future, if at all.

A proposal from the Maine Alliance for Sustainable Transportation suggests that none of those things need be true.

The group of alternative transportation advocates has proposed expanding the existing Zoom commuter bus that runs on the Maine Turnpike between Biddeford and Portland to include runs to Kennebunk, Wells, Lewiston-Auburn and Augusta.

Adding the service would be surprisingly affordable: Full implementation of the plan, in which involves buying buses and staffing them with drivers, would cost about $7 million a year, which would come out of toll revenues. That’s not a small amount of money, but it would be a fraction of what even modest roadway expansion costs.

It would could also happen quickly. If the Legislature passed a law the group proposes, the buses would be on the road in a year.

Whether it would have enough interest from riders to be viable is a subject that is worth more study.

The advocates say that it would, but ridership on the existing Zoom bus, along with all Turnpike travel, has declined recently, due to a drop in gas prices and a slowdown in the economy.

But there is ample reason to believe that either of those conditions are permanent, and it may be that a bus service on the Maine Turnpike, supported by toll revenues, would be both popular and a way to avoid future roadway projects.

The Zoom bus expansion program offers a practical transportation that is doable and affordable. It deserves a good hard look.