I wouldn't think they would house a Trackside AEI reader in a building, especially that size. The reader's I have seen are rectangular, about 2 feet high by 1 wide, usually mounted on a short section of antenna tower.
This is true of the antennas... think of AEI as being similar to toll passes with rfid technology. Same concepts, different applications.
I do not see any aei antennas, or any antennas for that matter. Alot of times the radio antennas on these shanties are NMO mounted right thru the roof... I don't see any here.
Given the lack of antennas, I am going to say that this would belong to other track circuitry.
I have many ideas, but without having knowledge of the area, I couldn't offer any more than a few wild guesses.
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