We also live in MD - about 1 hour from Lorton (depending on traffic of course!). On our last trip in August we considered the auto train home (we drove down) since the relatives we were vacationing with in FL were taking the train home. Well, after weighing the extra time it would take by train (we figured it would take approx 21 - 22 hrs. since it's an hour to Sanford, then you must be there 2 hours early so they can load your car, 16.5 hr. train ride, and hour to unload the car and an hour home - we can drive in at most 15 hours) and the expense (it was about $800 - we were 3 adults and 2 children, and this was with a deal where the children went for free) we decided to drive and skip the train. Granted we were tired driving home, but with 2 drivers we took turns, and we were home to sleep in our own beds that night (we left FL at 7 am). They got to sleep in their seats on the train (they opted not to get a sleeping car due to cost). Well, they all said it was an experience and they would NEVER do it again (the only one who enjoyed it was a 5 year old). They did not find it enjoyable at all. I know others find it fun, but I was certainly glad we skipped on the train after hearing how much they disliked it!
If you search for airfare and rental car deals (check out mousesavers.com) it may be cheaper to fly and rent a car than to take the train. We are flying on SW out of BWI (got a ding rate of $625 for 6 tickets) and renting a car (National $238 for 6 days) for our next trip in Dec, which comes out less that we would pay for 6 of us to take the train.