Rick:
That little innovation was started on the C&TS in the '70s. Seems 25 ton capacity frieght cars, when loaded with 4 to 5,000 lbs of people, tended to lock up their wheels a lot on the 4% grade coming down off of Cumbres Pass.
Empty freight cars would often do that too but freight didn't really care if there were some flat spots on the wheels. Passengers tended to complain about the noise and clumping. Hence the very ugly but utilitarian stripes on the wheels.
Wouldn't find it in Rio Grande days.