These are relatively new, but I suppose they make sense. Gettysburg is not a big town but given the number of people who travel here every year, it gets horribly congested. This gives the tourist a break from dealing with the many traffic lights, the small roads, the hassle of finding parking spots at every location. I'm all about mass transportation, if it's worth your time and its cost effective. The trolley option seems to be. The fare is $1.25 for one ride, $5.00 for 10 rides and if you're a senior citizen, it's only .75 cents. There are a few stops on the route, so you can get on or off whenever you'd like. Maps are available in most of the shops...
American Civil War Museum
By car. It's an hour and a half from BWI and Dulles, and Harrisburg International.
My preference would be to bike around Gettysburg, however, there are no accommodations for bikers, so you have to be very cautious. (FYI: It's illegal to ride on sidewalks.)
**UPDATE** Since 1999 there are two new bike rental shops. One is Gettysburg Bike Shop on York Street and the other Blazing Saddles on Chambersburg Street.
The best way to get to Gettysburg is by ones own car. Though Greyline Buses do make a stop here.
By car or on foot. If driving, there is an audio tour available to listen while driving through the park.