J. R. Simplot invested in a fleet of cryogenic reefers in the late 1980’s to move frozen commodities. These cars were cooled by liquid carbon dioxide that was slowly released inside the car, creating a cooling effect similar to the effect that occurs when operating a fire extinguisher. Because there is no way to reliably control the temperature, these cars were limited to frozen food use only, and did not replace mechanical reefers. I have read that the economics of CO2 made these cars fall from favor, and they were retired. Here a one-month-old example in in a train at Fogelsville, Pennsylvania.