During the course of my research, into the late 1960s and 1970s I have noticed many cars have a black and yellow symbol (circled) indicating the car is equipped with approved wheels
When did the dots start appearing? And when did their use stop?
Thanks,
Nick
according to what i have read, and i remember seeing these markings when i worked on the railroad the whole thing started in march of 1978. i don’t know the exact fault but certain wheels were banned due to a high rate of failure.
the dot / fra required inspection for the banned wheels whenever a car was interchanged or otherwise subject to being inspected by the car department.
cars with the banned wheels received a white dot in a black square and those without the banned wheels got a yellow dot.
all the bad wheels had to be removed from service no later than december 1978 therefor cars repainted or built from 1979 on did not have these dots since all the bad wheels had been replaced by then.
grizlump
Nick and grizlump -
I found this (below) at http://www.hosam.com/mod/rsdet.html#ui - at about 1/6 of the way down the page:
These stencils were applied to designate freight cars which had 33" wheels
manufactured by the Southern Wheel Company. These wheels were suspected of
failing in service and causing several serious derailments.
This FRA regulation began March 31, 1978 with the inspection of all 70 ton
or less cars which had 33" wheels.
Freight cars with this type wheels were stenciled 
with a 6"
white dot in a 12" black square.
Cars identified with the white dots could not be used in a train carrying
hazardous materials. Beginning December 31, 1978 cars that had the white
dots could not be used in any train. The wheels had to be removed and
replaced with wheels of an approved type.
Freight cars that had approved wheels were stenciled