Ted,

You wrote:

What percentage of the USRA single sheathed boxcars in their original
as
built configuration would have received AB brakes? The cars were
built
with K brake systems. Many cars were later rebuilt with steel sides
and
received AB brakes.

My question concerns as built cars, that would have been in use in the
late
1940's and 1950's with AB brake systems?

The ICC mandate to retrofit AB Brake Systems was probably the major
reason that the B&M chose to retire most of its #70000-70499 series of
USRA Double-Sheathed Boxcars between 1948 and 1950.

The B&M did not begin to retrofit AB Brake Systems on its pre-1935
Freight Car Acquisitions until after World War II - perhaps a practice
followed by many other roads. Cars that were not retrofitted were
removed from revenue service.

The number of cars in the 500 car #70000 series removed from Revenue
Service were by year:

Prior to 1948 25
1948 149
1949 215
1950 98
After 1950 13

So, 2.6% at most, of B&M's USRA boxes received AB Brakes - it was
probably less. B&M's last #70000 was retired from revenue service in
1955.

The decision not to retrofit with AB Brakes was also probably a cause
for the demise of the remnants of B&M's 1,500 car USRA #90000-91499 Gon
series, the 13100-13299 reefers and the 36' SUF Boxes which had survived
WW II. The B&M did retrofit about 3,200 cars after the War with AB
Brakes including its 1923 Design #71000-72999 boxcar series and its
#8000-8999 Quad Hopper series both acquired in 1929-30.

Other roads probably made similar decisions about their pre-1935
acquisitions - whether they could justify retrofitting with AB Brakes -
the alternative was to retire cars. The Pennsy's total fleet dropped 30%
from 237,813 on 12/31/1946 to 197,813 on 12/31/1949.

Hope this helps, Tim Gilbert