Two comments: That stack train, with one up front and one pushing- Is it empties? Or is this down grade so no need for much power? Also, one thing I am noticing about almost all oil trains I have seen is the tank cars are fairly clean. Older photos, they seem to usually eventually show at least some spillage up by the dome..
I would think modern EPA regulations would frown quite heavily upon leaks of any sort... much more so than in years past. It wouldn't surprise me if the maintenance, loading/unloading, and cleaning requirements of those tanks are quite strict...
I'm certain you are correct. But total absence of any stains is just interesting to note, after what I knew only a few decades back.