Ah. From the tone of your original message I thought your gf might need reassurance.
(and the comment on UP was really in response to another post farther done the thread)
In general, runaways were far more common with straight air (pre 1903). with improvements to automatic air, they became quite rare after about 1910. Most books have pictures of several because it seems to be the one time pictures *always* got taken! Sometimes it's a bit murky as to if it was a runaway or if the train was just going too fast.
A few (post WWI) I haven't seen mentioned yet: (dates are approx, off the top of my head)
There was a derailment on the Chile line(Barranca) in 1929. one on the RGS (Dallas Divide) in '43. C&S (Boreas) 1927(?) (Kenosha) 1936, and another on Boreas in 1935(?).
(Roughly) not more than once a decade on most lines. Crews (and the rule book) tend to be very, very picky about checking the function of the brakes before descending a grade. Since their lives depend on the brakes working correctly, this is not a surprise!
hank