What I can estimate is that the 1 car that is running on the 2 mile loop on any day might return in as little as 20 minutes or as long as 50 minutes. If it ever exceeds 10mph, I'm surprised.
Caught today in serendipity at Austell, GA, Norfolk Southern's Nickel Plate Road heritage unit 8100. This is another of NS's locomotives painted in historic colors that trace NS railroad history. [D5100]