Jeff,

A few thoughts on the questions your raised...I hope some of the guys can
further elaborate as well, especially on the operation of retainers.

<< Can you please elaborate on these?

1) How were classification yards "automated"? Not every yard was a hump
yard.>>

I am no expert on yard operations, but I do know that large numbers of
automated classification yards were built new (or improved from existing
yards) during the late 1940s into the 1950s by; SP, UP, NP, GN, NYC, etc.
Not all were "hump" type operations, but most were equipped with "modern"
push button controls to operate switches and retarder systems. The yards
were equipped with radio communications from tower to engine crews and ground
crews that helped to automate freight train make up. Many of these roads
were also partaking in the early computer age -- the use of the early IBM
machines for accounting and car tracking was credited for greater efficiency
of freight car tracking, distribution and train make up.

<<4) What's a "Release control retainer valve"? Should I infer that the
retainers could be set automatically without the brakeman's intervention?>>

Your inference is spot on. In 1941 the AAR introduced the "four position"
retainer. Prior to that time the standard retainer was a three position with
the slowest bleed down time of around 60 seconds. The newly designed fourth
position contained an orifice that was the size of a number 60 drill bit
(which many of us are familiar with via our modeling). This fourth position
allowed a bleed off time of around 86 seconds (average). This allowed
retainers to be set one time as trains were made up in yards with decreased
further adjustment between points. The slower bleed off time made great
strides towards reducing train "slack" action. Among the drawbacks was the
smaller orifice was prone to clogging which would lead to brake "drag"
causing overheating of wheels especially on fast freight operations. Though
that problem is mentioned in AAR publications the special attention to
maintenance of the retainer must have eliminated most of the problem.

I don't have the data in front of me, but believe this retainer became
mandatory with new construction and rebuilds sometime around 1947. It was
also recommended that the new retainer be installed along with the retrofits
of "AB" brake systems. The new design also incorporated a permanently
mounted bracket (on the car body) from which the retainer could quickly be
removed for maintenance with the removal of two bolts. The AAR also designed
a "retrofit" that converted the three position to a four.

<<5) I assume this [ref: radio communications] simply means that brakemen
didn't have to stand on top of the cars to relay signals from the rear end to
the head end.>>

Seems logical...I would think that the hand signals were pretty much useless
once a train length was approaching 60 to 100+ cars which were common from
the 1930s on.

Regards,

Guy Wilber
Sparks, Nevada