Take Amtrak’s Capitol Limited from DC to PGH. It gets in late, but there is a bike-friendly hotel a couple of easy blocks away. The train has a special place for bikes that doesn’t require disassembly, It’s very popular, so reserve bike spaces way ahead of time. The start of the GAP is an easy ride from the hotel.

Let me know if you have any other questions about the GAP. I’ve done it 3 times as part of longer tours.