My fiance and I are visiting his sister in March. She lives close to Baltimore. I have never been to either place so I am concerned about the travel time from one place to the next. I originally thought that we could spend about three nights with her and three nights in DC. I assumed that travel from Baltimore to DC would be easy and that we could visit DC for the three days we were in Baltimore. Is this possible or should I make other arrangements? Thanks in advance.

Where exactly in Maryland near Baltimore -- south of Baltimore? From downtown Baltimore to the sites in DC is about an hour driving distance.

Very easy drive between certain parts of Baltimore and DC if you time it around rush hours. BUT, if you get caught in a backup because of an accident, you will wish for that room in DC.

If it's during the week, the MARC trains are a great, relatively stress free and cheap way to get between the towns ...

As a local, I'd go with the PP--MARC trains during the week. We prefer to drive to a metro stop on the weekends and take it in.
On occasion, we will drive in--usually about an hour and we are west of Baltimore. In reality, it's only about 40 miles.

Mo