At first I thought these were really refrigerator cars but upon closer inspection they are insulated box cars used for hauling milk. There are no ice hatches on the roofs of the cars either. You can see the word milk on the car in the right corner of the photograph. Its wheel set or "truck" is a beefed up express truck capable of higher speeds then the convention freight car trucks of which we see side frames lined up in the foreground. This was necessary as these cars were usually hauled on passenger trains. These are excellent photographs.