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In 1900, there were about 8,000 registered motorized vehicles in the United States. Forty years later, their number had soared to around 32.5 million, or one automobile for every three Americans aged 15 years and over (this ratio rose to 1.7 in 1960, and then to 1.09 in 1985). Such an increase in the number of vehicles and the resulting traffic (especially in urban areas) prompted State engineers working for the Bureau of Public Roads, a federal agency, to carry out large traffic surveys in the 1920s and the 1930s, with a view to designing new rational transportation systems capable of fulfilling the mobility needs and desires of American households. From the mid-1940s onwards, a new kind of traffic survey named Home interview emerged as a major tool for obtaining information about the mobility patterns of American citizens. This article tells the story of Home interview (1940s-1960s); it describes the main characteristics of this survey tool as well as its evolution over time, while identifying the conditions of emergence of Home interview and the various goals its users sought to pursue through it.