Everyone here has added important elements to the story of the evolution of the movement of grain in sacks in 1900 to bulk shipments in box cars and finally 100 ton coverd hoppers in the 1960s. Changes in car building, changes in the labor market and investments in shipping and receiving facilities are all a part. I'll add a few more elements to consider.
Two more important pieces to the economic puzzle were the development of trucks and farm to market roads. Thousands in miles of paved roads were built in rural America in the 1920s, 30, 40s and 50s. And by the 1940s the truck building industry has advanced to the point where farmers and freight haulers could move loads of nearly the size we see today and at similar speeds.
Here are a few views of the Washington Co-Op Farmers Association feed mill in Tacoma in the 1950s.
The first photo from 1953 shows box cars being loaded with sacks of blended feed as well as a Kenworth tractor hauling a load of bagged feed. A truck is also being loaded with bulk feed. Bulk shipments of grain are received in box cars on the other side of the mill.
The next photo from 1958 shows new construction completed to serve the Co-Ops growing bulk feed market. Note that a bulk truck is being loaded with blended feed along with a box car and a new 70 ton covered hopper.
Perhaps the single most important reason that covered hoppers did not come into widespread grain service earlier is that government regulation prevented grain shippers and receivers and the railroads from being able to get a payback from investment in new facilities and cars. The Southern Railway had to essentially sue the federal government to be allowed to offer lower rates to customers for shipping in multiple car lots of grain in covered hoppers. Until the railroads had the ability to pass along part of the cost savings from multiple car shipments of 100 ton covered hoppers the grain shippers and receivers lacked an incentive to invest in larger and more modern facilities.
To get the full benefit of unit grain trains takes bigger grain elevators. Bigger elevators are further apart than older smaller elevators to gather enough grain. Farmers have to drive farther but with bigger and faster trucks they can do it and big elevators could offer a better price than smaller elevators due to the shipping cost advantage that came with unit trains. A better price for the farmer made the longer truck haul worth the extra effort.
Reduced cost to the railroad meant reduced cost to the shippers and receivers and a better price for the farmer. Railroads, elevator operators and farmers all had to make investments to take full advantage of new technology. But just as soon as the government got out of the way it happened. Within two years of the landmark Southern Railway case car builders like Pullman-Standard, ACF and Magor were all selling 100 ton covered hoppers by the thousands.
