Officials hope the major schedule shift will also accommodate an influx of personnel to Fort Meade and Aberdeen expected by September.
The changes to the Maryland Area Regional Commuter (MARC) service, which are scheduled to take place March 14, will add more frequent trains with fewer cars during peak periods.
"This will minimize stress on our locomotives," MTA Chief of Staff Simon Taylor said, and reduce the time it takes to board and off-load individual trains.
But there will be a net gain of 1,000 seats between 6 and 9 a.m. and between 4 and 7 p.m., he said. There will be two additional round-trip trains in the morning and two in the afternoon. MARC operates only weekday service.
"We realized we needed more service during those hours," said John Hovatter, director of MARC train and Commuter Bus services. He said 70 percent of passengers between Baltimore and Washington travel during those periods.
Under the new plan, eight trains with six or seven rail cars each will service the Penn Line. Service is now provided by six trains with seven to nine cars each. MARC's Penn Line primarily operates between Union Station and Baltimore's Penn Station, although some trains run to Perryville.
Taylor said the changes will not require buying new rail cars.
The decision to revamp the schedule "was based on a number of factors," he said, including reducing the engine breakdowns that occurred on the Penn Line last summer.
In the most extreme incident, 1,200 riders were stranded on a hot train without air conditioning for more than two hours.
Ten people were treated for heat-related problems, and three others were taken to the hospital.
A report released in December pointed to a series of "organizational failures at multiple levels." The incident highlighted what many MARC passengers describe as deteriorating service in recent years.
MTA spokesman Terry Owens said ridership on the Penn Line has grown 95 percent from fiscal 1996 to fiscal 2011.
The agency did not have daily ridership numbers for the line immediately available.
Rafael Guroian, chairman of MARC's Riders Advisory Council, said the changes were overdue.
"If nothing else, the changes add capacity that, frankly, the Penn Line has needed for some time," he said. "Hopefully people won't be standing in the aisles any longer."
But Guroian warned that "no one knows if these measures will solve the cause of the breakdowns. We hope it's going to help. There are going to be many more trains on the corridor, and there's the potential for congestion. But this move needed to happen."
Owens said the MTA worked closely with Amtrak, which operates the Penn Line and its own trains on the same tracks, to determine the new schedule.
The MTA will monitor the service to see whether adjustments are needed, he said.
Officials hope the changes will also help accommodate new commuting patterns expected when thousands of Defense Department jobs shift to Maryland as part of the Base Realignment and Closure process.
More than 7,000 positions have already moved to Fort Meade, and the process will bring about 5,500 new workers to the base by the September BRAC deadline. The Defense Information Systems Agency is relocating 4,300 people from Arlington County to Fort Meade.
MARC will operate a "reverse commute" train in the morning that will leave Union Station at 6:15 a.m. and arrive in Aberdeen by 7:42, "to meet the work needs there," Taylor said.
The MTA also plans to store some trains at the rail yard at Martin State Airport, to reduce congestion on the tracks at Union and Penn stations, Taylor said.
There will also be express trains to Odenton in the afternoon, Hovatter said, a request made by passengers. There will be no changes in fares, he said.
To put the new schedule in place, it must be approved by the Maryland Board of Public Works on Feb. 23, MTA officials said.
The MTA plans to begin a "major public outreach effort" Monday, spokesman Terry Owens said. The campaign will include meetings with riders at MARC stations, e-mail notifications and information on the MTA Web site. The state also plans to place a large number of personnel at stations on March 14 to help passengers, he said.
The MTA said it plans to coordinate changes with local jurisdictions and agencies that provide connecting transit service at commuter lots and other locations, such as Baltimore-Washington International Marshall Airport.
Owens said the MTA is also in talks with CSX, which operates the Brunswick and Camden lines, about possible schedule changes. The Camden Line runs between Washington and Baltimore, and the Brunswick Line operates between Washington and points north and west, including Frederick and Martinsburg, W.Va.