The Maryland Transit Administration’s MARC trains, which run only on weekdays, are expected to start running between Washington and Baltimore on weekends this year.

The agency is looking at adding “eight to nine round trips per day” between Washington’s Union Station and Baltimore’s Penn Station, said Terry Owens, a spokesman for the MTA.

Passengers, businesses and others “have talked about MARC weekend service for years,”, he said. It’s unclear when it will start. Owens said the goal is to begin by the end of the year, though it could be sooner.

Amtrak owns the Penn Line tracks, and the MTA, which contracts for weekday service, is negotiating on weekend schedules.

The service expansion comes as part of legislation signed by Gov. Martin O’Malley (D) last week that raises the state’s gas tax.

Officials say the revenue boost provides $1.2 billion for road and transit projects, including $100 million for MARC improvements, as well as money for the Interstate 270/Watkins Mill Road interchange in Montgomery County.

The MARC money will do more than add weekendservice. There will also be 10 new locomotives and two additional weekday round trips on the Camden Line.

But the weekend service is a major shift, which could be a boon to people who work on weekends or need to reach Baltimore-Washington International Marshall Airport.

“We’ve always been asking for it as riders, and it’s always been a matter of money,” said Rafi Guroian, chairman of the MARC Riders Advisory Council. “People are relieved that it’s come.” MARC trains will be a very affordable way” for weekend travel between the two cities, he said.

Weekend MARC service has been attractive because of the cost. Amtrak charges between $22 and $32 for Saturday trips between the District and Baltimore; on MARC it would be $14.

The cost won’t change when weekend service begins, Owens said. And weekly and monthly passes would be honored. The bill signed by O’Malley does, however, include a $1 MARC fare increase for next year, he said.

The new service could also benefit BWI. “We’re thrilled with the addition,” said Jonathan Dean, an airport spokesman.