This link [1] says the median US train is 5,400 feet, and this link [2] quotes an intermodal railcar for 53-foot containers at 67 feet, 9 inches; although 40 foot containers are the most common size; let's use 60 feet as a round number car length; that would put the median train at 90 cars; the 90%ile train is 9,800 feet or 163 cars by my length estimate, and 99%ile was 14,000 feet or 233 cars.

Probably depends on the specific route, but 200 cars doesn't seem unrealistic.

[1] https://www.aar.org/article/freight-train-length/ [2] https://www.mrc-rail.com/railcar-results/intermodal/

They are unwieldy and because of their length they're now too long for the sidings constructed to allow trains to pass each other causing scheduling issues. The whole rail industry in the US is slowly choking itself to death on it's own short term profit motives.