Amtrak is offering a Black Friday sale where you can purchase a train ticket with up to a 30% discount. This is a 4-day sale that will run between Black Friday and Cyber Monday. This is valid for travel starting December 1, 2017 through March 31, 2018.
No promotion code is required and the discount will automatically appear. You can check out the discount on their Black Friday page where some routes are 25% off and others are 30% off.