>If you've already got the capacity for the traffic you have, plus some, why build additional capacity?

If you go back and read UP's announcement of PSR - it says NOTHING about improving service, efficiency, service or growing the business. It was strictly about cutting costs and operating ratio which has resulted in them driving off some business they didn't consider profitable enough. What the college geniuses don't realize, is that railroading is EXTREMELY expensive with a high fixed base cost. The incremental costs per car if you're under about 80% track capacity doesn't really count for that much in direct costs, but does help spread the fixed costs between more carloads.

The dirty secret is that BNSF has apparently instituted a type of PSR, at least in the Pacific Northwest. Last I heard, train crew with less then five years seniority are furloughed, despite crew shortages.

There is of course a general rail traffic slump which has been in effect for a while. Not sure if there is one cause, but it seems odd considering how hot our economy supposedly is unless it is a precursor of things to come. Possible contributing factors are coal falling out of favor and the resistance of US Pacific coast ports to allow new export facilities, the trade war with China (did everyone import heavy early to beat tariffs?), the earlier Midwest flooding, the normal boom and bust of grain, autos, building materials and oil/frac sand - not to mention traffic lost to PSR.