Originally Posted by You want to go where?
Toddr4fun did provide the real answer to your question. Many of the tracks at Washington's Union Station have raised platforms. But those tracks which go under Union Station to continue to Richmond, Newport News and other points South and West do not have raise platforms. Obviously, all trains going to or coming from these destinations use these tracks. Occasionally, trains originating or terminating in Washington use them as well.
You are correct that all of the tracks on the lower level, those that run under the station and into Virginia, have low level platforms. Those tracks have the highest numbers at the station.
However, there are also a few tracks on the upper level that also have low level platforms. Most are high level on the upper level and normally Amtrak tries to use them for all Amtrak trains other than the Capitol Limited. But occasionally, when there are problems Amtrak's other trains do end up on a low level platfroms. The only exception to that would be Acela Express trains, which cannot use low level platforms.
The Capitol Limited by the way is one of those long distance trains that is a double decker train. It can only use low level platforms, as the door is designed only for low level platforms. If you tried to exit at a high level platform, you'd actually have to climb up about 3 feet to reach the platform.