Ah, Capital Beltway station. Now that brings back lots of memories.
I grew up in the city of New Carrollton and spend many a day sitting on the platform watching GG1's, Metroliners, E33 and E44 pass by. Later on I hired on with Amtrak as a tower operator on the then Baltimore division. One of the towers I worked at was "Landover Tower" which controlled the signals and switches at Capital Beltway. When Capital Beltway closed, Landover then controlled "Carroll" interlocking which is located where Capital Beltway used to be. A little later on in my career with Amtrak I controlled both "Carroll" and "Landover" as the CETC 1 dispatcher in Philadelphia.
The station was built as part of the Metroliner High Speed project back in the late 60's/early 70's. There were two platforms. One was between No.1 and No.2 track serving No.2 track. The other platform was along side No.3 track. Both platforms were connected by a tunnel that connected to the station builting. The station building was a green (Penn Central green?) pre fab building that had a small ticket office, two restrooms and a waiting room that held maybe 20 to 30 people.
Here is a photo that I found by Googling "Capital Beltway Station" -
The photographer is standing on the No.2 track platform looking north. The gauntlet tracks can be clearly seen in this picture with the train on the platform track. The highway bridge in the background is the Capital Beltway bridge.
As you can see in the picture, the platforms were wooden with a blacktop overlay. Towards the end in the early 80's the platforms started to sag noticably.
Today not much remains of Capital Beltway. The tunnels have been capped and the platforms torn down to make way for the switches at "Carroll". The station building still stands and is now used by the Maryland DOT. The parking lot is used to park highway maintanence trucks and a large salt dome stands at the northend of the lot.
As far as the Lanham MARC station is concerned, MARC trains stopped there until the station at New Carrollton opened in 1983. The station was located at the old Lanham road crossing (which was closed when the Metroliners started running). MARC trains never did stop at Capital Beltway.