When I moved to Elkridge almost a year ago and started commuting back and forth to NIH, I wasn't able to find much information online about the specifics of riding the MARC. On my first attempt, I boarded the wrong train coming home and only just missed sailing off to who-knows-where. It took time to figure out the best places to stand, the kinds of delays to expect, etc. In the interest of perhaps sparing someone such inconveniences, and at the risk of thwarting some adventure, I offer here a hopefully simple (but wordy) guide to my particular commute.
First leg: Elkridge Crossing to Dorsey MARC Station
I live in the Elkridge Crossing neighborhood, near the corner of Rt. 1 and Montgomery Rd. The public transit options include HowardTransit Purple Route, MTA Commuter Route 320, and MTA MARC Train Camden Line. The first two stop within walking distance, but neither is of much use for my commute. The Purple Route first run is at 7:00 a.m. I could catch the 320 a little after 6:00 a.m., but I'd still have to walk 15 min or more from Rt. 1 and Dorsey Rd. to the MARC station. The earliest I could start work is 8:00, which would get me back too late to catch the last 320. The last rush-hour Purple Route would get me home no earlier than 7:00 p.m., just when the kids were going to bed.
So, I bike to and from the MARC station. It takes about 20 min. each way--maybe a bit longer in the evening, since there's more uphill. As I've commented elsewhere, Dorsey is not designed well for bike access. You have no choice but to come down Rt. 1 (there are some more roundabout alternatives, but almost none of them keeps you off it for long), past the station at Rt. 100, turn left on Dorsey Rd., left again on Douglas Legum Dr., right on Deerpath Rd., cut through to the station parking lot, and lock your bike up down by the station itself. I don't know how much the lockers are. I'm cheap, so I just leave my clunker at the bike rack, and so far nothing has happened to it.
NOTE: St. Denis MARC Station is probably about the same distance away, in the opposite direction. I can't comment on getting to it because I've never tried. The train stops there infrequently, so for my schedule it would be impossible.
Second Leg: Dorsey MARC Station to Washington Union Station
I take the first train of the morning, but I haven't noticed much difference on the rare occasion that I've taken a later train. Normally you wait on the platform closest to the station to head south. If the signal is red, it may mean that the train will come in on the opposite track. There are loudspeakers, and sometimes you'll get a message indicating if there's a delay or track change. You can also sign up for e-mail notifications, which I would recommend if you carry a blackberry or some such device.
The main thing you need to know about riding the Camden Line is that it runs on CSX (freight) tracks. Freight traffic seems to get the priority in most cases, so sometimes a train will have to wait for something (never sure what) to happen. Sometimes you'll have to change tracks to accommodate a more important schedule. Then there are signal problems, switching problems, and the ubiquitous "heat restrictions," where CSX limits the speed of the MARC trains any time it gets over 90 degrees. Basically, expect to arrive late, and be appreciative if you arrive on time. Afternoons tend to be worse, but it won't be long before you spend half an hour standing on the platform in the morning, waiting for a train that's delayed for some vague reason.
The car closest to the engine is usually the quiet car. At some stations, the platform is too small, and you have to board or exit through certain cars. Aside from that, if you want to make the best time possible, identify the car that will get you closest to where you want to go. In the morning, you want one of the front two cars. Normally you can only use the rear doors in the first car or the front doors in the second car. Since they're next to each other, it makes little difference which car you actually ride in--just get as close to the doors as you can. You'll want to wait somewhere around the far end of the second bench on the platform. If you can't get a seat close to the door, you can do like a lot of people and stand in the aisle after Riverdale.
Union Station is the end of the line, so there's no danger of sleeping through your stop. One side of the aisle has two-seaters, the other has three. I prefer the two-seat side if I don't have to go far to get it. The aisle seat on the three-seat side is too short to sleep comfortably, and it's awkward to sit down in the middle seat if there are only two passengers in the row. If you don't mind sitting by the window, the side doesn't matter much. The bathroom is usually in the end car, though personally I've never used it. I usually go when I get to the train station.
When you exit at Union Station, walk toward the front of the train. Once through the doors, head right, then down the escalators, and through the turnstiles. If you need the men's room, it's straight through the doors from the platform. I think the women's room is further down to the left.
Third Leg: Union Station to Medical Center
There's good information on the WMATA site about riding Metro, so I'm not going to say much here. If you have time, head all the way down toward the opposite end of the platform. Wait along the railing next to the last escalator structure. By boarding the train there, you'll be just about in position to head right up the escalator when you get off at the other end. I usually get out of my seat at Bethesda and get in position by the door.
Fourth Leg: Medical Center Metro to Building 31
I usually walk up the escalator to save time. Keep walking straight ahead. Visitors have to go through the Gateway Center to your left. Anyone with a badge can walk down to the other end and enter through the turnstiles. Once inside, you can take a shuttle or walk. If I arrive more or less on schedule, I can usually tell by the time and the number of people waiting whether the Campus Shuttle has already come by or not. If it has, and I don't see Mid-Pike, I'll walk. Otherwise I'll usually wait. Mid-Pike is faster, since it goes straight from the gate to 31. Campus is more regular, because it doesn't have to deal with outside traffic. It also comes more frequently.
I take the Rockledge or Executive Plaza Shuttle back to the Metro. Campus Limited would also work. Again, I jog down the escalator, and if there's a wait, I walk all the way to the opposite end of the platform. The further you can get to the front of the train, the better. The escalator at Union Station will be just outside the front door, and it's usually mobbed. Get a seat right by the door, or stake out a spot to stand somewhere around Metro Center. Doors open on the left.
Up the escalator, through the turnstiles, up the next escalator, then straight ahead. Check the screen for your gate. This is important. There are electronic displays at the end of the tracks, but they don't always work. More on that in a bit. I usually run to the bathroom if I have plenty of time, so I don't have to again before riding home. There's also a display in the passenger waiting area, if you didn't already get your gate number. Everything's Gate A. I think that's all MARC trains--definitely all Camden.
Now, here's the tricky part. If the track displays are working, take a quick look at yours. It should say "far north end," if the trains are stacked. Sometimes they'll put one train in front of another. Unless you're super early, that almost always means yours is out on the end. You'll have to walk *past* the train behind it. Most of the time, the rear train isn't boarding yet, so you can tell by the closed doors that it's not yours. If it is, check the size of the cars. Camden trains are mostly single-decker, occasionally with one double. If you see a lot of double-decker cars, keep walking. Once you've been riding a while, you'll get to know the faces on your regular train and the conductors (though they do change). When in doubt, ask. Ask the conductor if possible; ask people around you if you don't see one. There will usually be an announcement at some point before the train pulls out, but if you got on the wrong one, chances are pretty good you'll miss the one you wanted by the time you hear anything.
This time, you want the rear of the train. I usually go for the second-to-last car, because they fill up faster, and the bathroom in the last car pushes you back from the door. If you don't get a good spot, you can move forward once people start clearing out, or stand in the aisle after Savage. Just watch where the conductor is hanging out, so he'll have room to get by. Once you exit, walk around the rear of the train and across the tracks back to the station side. If you need to use the bathroom or wait for a ride, the doors facing the parking lot should be open.
I ride my bike back the way I came, with one exception. I take Old Washington Blvd at the split to simplify turning left on Montgomery Rd. Traffic is more of an issue later in the day. You have more shoulder to work with, but don't get too comfortable with it. It will vanish into a turn lane or a curb without much warning.
NOTE: A word about MARC tickets. There are ticket machines in most stations. I don't use them, because I get a subsidy and you can't pay with vouchers. The Amtrak counter at Union Station will sell MARC tickets, but for my purposes it's very inefficient. Because I don't commute every day, I buy one-way tickets. Because I get subsidy vouchers, I buy large quantities at a time. At a manned MARC counter, this is pretty easy--they just punch in your destination and the number of tickets, and hit print. At the Amtrak counter, they have to key and print each ticket separately. Make sure to budget time if you have to buy your tickets that way.