In a slightly surprising piece of news, the Southeastern Railway Museum outside of Atlanta - which has a small collection of electric cars but is mostly focused on steam road equipment - has acquired a car from the initial order for Atlanta subway cars. MARTA 509 arrived at the museum on Wednesday and will be placed on public display there, according to this press release.
This is actually a relatively significant acquisition, historically speaking. First, of course, it has local importance. Car 509 is the first and only MARTA car in preservation, and given the paucity of trolley museums in the southeast and the difficulty in putting large subway cars like this to practical use in a museum setting, may very well be the only MARTA car in preservation for quite a long time. Amazingly, I think it's also only the second electric railway car from Atlanta ever to be preserved intact after retirement (you may have to think hard to guess the first), at least if you only count cars still around today.
Furthermore, this car has some national significance too. During the 1960s, 1970s, and 1980s, several cities built all-new heavy-rail subway systems, including not just Atlanta but also San Francisco, Washington DC, and Los Angeles. Other than a pair of WMATA cars that have supposedly been squirreled away for safekeeping, but to my knowledge have not yet appeared publicly as historic artifacts, this MARTA car is the first car from any of these modern subway systems to be preserved in the US. (I say "in the US" because this preserved car from the Montreal Metro is also from a modern subway system, albeit a very unusual system built for rubber-tire cars.)
EDIT: Thanks to Richard Schauer for sending a link to this video about the history of car 509 and its donation to SERM. I was quite impressed; the video has a good mixture of technical/design history of the car and general background information on MARTA.