Search

The automobile transformed life in America, but there has been very little quantitative analysis of the diffusion of the automobile in the 1920s and 1930s. In my first chapter, I compile a new county panel data set with car registrations and highway miles for the 1920s and 1930s to examine the interaction between automobiles and the building of highways in three states Indiana, Pennsylvania and Wisconsin. I find that a 10 percent increase in state highway miles leads to a one percent increase in car registrations. If the Federal government helped states double their state highway miles in 1930, the number of automobile registrations in 1942 would have increased by about 63 percent at the county level. Using the same instrumental variable with Chapter 1, I discuss the relationship between the diffusion of motor vehicles on farms and farms' access to good roads in Chapter 2. A ten percent increase in farms' access to hard roads leads to 0.8 percent increase in the number of automobiles on farms, and three percent increase in the number of trucks on farms. The impact of having access to gravel/shell/clay roads on farms' truck adoption is also about three times higher than that on farms' automobile adoption. Together with the rapid automobile adoption, deaths from infectious diseases have declined in the U.S during the 20th century. The 3rd paper examines the relationship between rapid automobile adoption and the fall in mortality rates, with a focus on infant mortality in the early 20th century. Cars replaced horses and reduced the number of horse stables in the cities, along with the manure that nourished generations of flies, the key carriers of the germs and bacteria responsible for infectious diseases. This trend helped to improve sanitation on a macro (urban) and hygiene on a micro (individual) level, especially in large, crowded cities. This, in turn, drove down deaths from those diseases.