From the East - Pennsylvania Turnpike - Exit 189 (Willow Hill)
From the exit, turn left onto PA 75. At the blinking light in Spring Run, turn left onto PA 641. Follow PA 641 to its end at Shade Gap. Turn right on US 522 to the only traffic light in Orbisonia. (In Orbisonia, 522 is Ridgely Street. Pizza Star is on the near-right corner and Community State Bank is on the far-left corner.) Turn left on PA 994. (In Orbisonia 994 is Elliot Street.) Cross the bridge over the Blacklog Creek and into Rockhill Furnace. (You are now on Meadow Street.) Pass Cummins Road on the left at the end of the bridge. (Cummins road provides automobile access for photographers for about a third of the trolley line.) Pass the Church of the Bretheren, the Rockhill Elementary School, and the Rockhill Furnace Post Office, all on your left. You will see the East Broad Top Railroad station ahead on your right but don’t go that far. Just beyond the post office cross one track only and turn left onto the gravel road just before the other tracks. You are here. The Meadow Street Trolley Platform and ticket booth are on your left.
From the East travel time is exactly the same as if you were to take Exit 201 (Blue Mountain), but instead of crossing the first mountain, you will tunnel under it, drive a bit faster but further, and pay a higher toll.
If you happen to find yourself continuing past Exit 189 (Willow Hill), you can take Exit 180 (Fort Littleton), but this adds about 20 minutes to your trip. See "From the West - Pennsylvania Turnpike - Exit 180" for directions to the museum from Exit 180.
Or use Google Maps.