This thesis studies the factors leading to the modal shift from rail to road in Baltimore’s farm to city milk transportation in the 1920s. It draws on histories of transportation, public health, food, and business to maintain that progressive public health regulation, driven by calls for reform of the milk supply, created an oligopoly for which trucks better suited vertical integration goals. This research highlights the relevance of public health policy to the study of transportation regulation and modal competition. Secondarily, this thesis establishes railroads as a primary actor in the 19th century rise in urban milk consumption.