Passengers on the Matthew Hayes operated by the Potomac Riverboat Co. cruise from Alexandria to Georgetown passing the national monuments. (Jonathan Newton/The Washington Post)

The cost of running regular ferries between Alexandria or Reagan National Airport and the Southeast or Southwest Washington would be about $6.4 million per year on each route, not counting the cost of terminals, docks, dredging or land transportation connections, a consultant said Thursday after a presentation to the Northern Virginia Regional Commission.

But four basic routes, out of 26 studied, “have enough market potential that they could be pursued,” said Tim Payne, a principal in Seattle-based Nelson Nygaard Consulting. “The market exists, we just need to find a little more strength to make it financially sustainable

After a year-long study, commissioned by the organization of governments, Payne concluded that water taxis originating in Alexandria or at the airport would find plenty of commuters seeking to avoid the congestion of highways, subway and rail, especially if they are bound for the booming Southeast or Southwest areas of Washington.

The most likely first test of the concept would be between Alexandria and Joint Base Anacostia-Bolling in Southeast Washington, Payne said. The commute would be restricted to those who could prove they work at the base or the nearby headquarters for the Department of Homeland Security on the grounds of St. Elizabeths Hospital. If boats ran every 15 to 20 minutes during weekday peak travel times, Payne said between 300 and 500 trips would result.

“The U.S. Navy is considering very heavily making an investment in this service sooner rather than later,” Payne said.

Naval officials at the base could not be reached for comment Friday.

Other than that route, creating a system of water transportation in the Washington area would likely require taxpayer funds, Payne said. He said he could not estimate how much it would cost to build shoreline facilities, because it differs so much from site to site, but a 2009 study put the capital cost of a Woodbridge-to-Washington route at $30 million, and an additional $20 million for a Maryland-to-Virginia crossing. Neither of those routes was included in Payne’s recommendations, however.

“There isn’t a private entity in the United States that has been able to start up without some public subsidy for shore facilities,” he said.

The elected officials who compose the Northern Virginia Regional Commission asked few questions Thursday. Fairfax County supervisor Jeff McKay and board chairman Sharon Bulova said they were disappointed that Fort Belvoir military officials declined to open part of their Potomac River frontage for a water taxi due to security concerns. About 42,000 people work at the base.

“For Fairfax County, without Fort Belvoir, I’m not sure how useful this is to us,” Bulova said.

The decision by that base, and disinterest from the Quantico Marine Corps base, means that creating a long north-south commute from the Woodbridge area to Washington is not economically sustainable without government subsidy, Payne said. But the outlook is much brighter for inside-the-Beltway water commutes.

“If we could get some of the shorter routes up and operating, that would do a lot to... build confidence that this is a transportation mode to get me to work everyday,” Payne said.

Alexandria, which already is home to the private Potomac Riverboat Co., would be a major winner if a system of water taxis ever comes to pass. That company, which helped fund the study, carries about 300,000 passengers each year for tourism-related cruises to Mount Vernon and the Mall and chartered special event cruises. It started a water taxi service to National Harbor in 2007.

An Alexandria-based service should provide every-15-minute departures from the Old Town Alexandria docks seven days a week to the airport, Washington and Prince George’s County, with fares in the range of $8 to $10, Payne said. Ridership on each route would be 1,100 to 2,000 passengers per day.

An expansion there might require more dock space and maintenance facilities, president Willem Polak said earlier this month. Parking, which Alexandria city council member Del Pepper asked about Thursday, could be handled with remote lots or garages with buses bringing commuters to the docks, Payne said.

Creating a terminal at the airport would probably require dredging near the shallow Four Mile Run at the south end of the airport, as well as building a dock and shelter, Payne said. That’s the sort of thing that will be addressed in a subsequent implementation plan, and the commission will also decide next year whether to go ahead with plans to create a concept for how to pay for such a system of commuter water taxis.