Antenna

[Eriediamond]

I was reading the topic on ballast when this just happen to pop in my head, so this is one of those crazy not too important questions, but one that someone in the know might answer. A couple of years ago I was stopped at a grade crossing and a train was working a gravel company so had to wait while it was backing into the siding. Anyhow I noticed some of the cars ( they discharged the gravel out the side rather then like a regular hopper) had antennas on them on one end at the top on one corner. They looked almost like an automobile antenna. Not all the cars had them, but the majority did. Anyone know the purpose for these?