The Baltimore Business Journal has a fairly detailed breakdown of how State officials plan to use $360 million in stimulus funds to update MARC and Amtrak systems throughout Maryland. (The article is speculative- "if Maryland is awarded the funds"; though it doesn't explain the approval process. Any stimulus nerds out there feel free to post an explanation of the process.) By my rough estimate about half of that money, or $134.3 million will benefit MARC.
MARC's Brunswick Line will be the most direct beneficiary of the funds, according to the BBJ:
"$18.3 million for MARC Brunswick Line signaling improvements. The funding would update railway signaling between Silver Spring and Brunswick for expanded capacity and would improve service reliability on the CSXT Metropolitan Subdivision, serving intercity passenger rail, MARC and freight trains. More indirectly, the funds ($36m) will make your MARC commute less painful by relieving congestion at Union Station, which often account for delays at the end of the work day."
Many of the earmarks are forward-thinking, an element that would please Rafi Guroian, the chairman of MRAC (short for MARC Riders' Advisory Council.) During an interview at Union Station a few weeks ago, Rafi explained his vision for the council: "I guess we're trying to make sure that potential MARC riders of the future, on lines that don't exist are represented. Because otherwise there's no voice for them." While the state's Dept. of Transportation is not proposing studies for new lines per se, it has asked for about $100 million for track expansion and improving safety and capacity on the rails.