Use of 40 ft Boxcars through time

[Brakie]

Can anyone give me a brief history of the demise of the 40 foot boxcar? I know there was a point in time when they were the predominant length of car used, then the 50 footers started edging them out. Perhaps give me a rough percentage of 40 fotter versus 50 footer for each decade? Just trying to get a feel for the mix I need to use on my layout.

Age is what help the fall of the 40' boxcar since most had passed 30 years of service and the need to remove the roof walk and lower the ladders per the new Federal rules and compliance date so,railroads went with new 50' ,50'6" and 60 footers instead of a massive rebuild program..Then the truck trailers was getting longer as well.

So age and a Federal mandate killed the 40' boxcar.