This study examines how the relationship between speed and danger was conceptualized in Iran during the second quarter of the twentieth century. Specifically, it traces discourses and policies related to railway accidents. Acceleration experienced in Iranian society intensified in the early twentieth century as new modes of transport became part of Iranian daily life. With the development of transportation infrastructure, including Iran’s first long-haul railway, the construction of highways, the coming of the automobile,and the beginning of bus service in the post-WWI period, the speed of travel increased exponentially in the context of the rise of the centralizing Pahlavi state. A Tehran to Ahvaz trip that took almost a month at the beginning of the twentieth century took only one day by train in the late 1930s. As the speed of travel increased, however, deadly traffic and railway accidents became highly visible. From mangled trucks and wailing mothers next to dead sons on the roadside to dismembered bodies on railway tracks, death haunted travelers and transport workers who moved across space for various purposes using old and new modes of transport side by side. By analyzing discourses of railway accidents in the publications of the Ministry of Roads and the Iranian Railway Organization, this paper argues that the association between speed and danger was not necessarily inherent. Rather, it was the expert knowledge of the first generation of Iranian techno-scientific elites in such fields as engineering and psychiatry that played a pivotal role in defining the danger of speed as a social problem caused by human factors. Their intervention was linked to the desire to carve out their professional position vis-à-vis not only Euro-American engineers but also rank-and-file railway workers as objects of social reform. By using Iranian archival documents, this paper also explores how the authority to define the root cause of railway accidents sometimes translated into specific policies. What was considered adequate training for workers, especially locomotive engineers, who should be blamed in specific cases of accidents, when and how much workers should be compensated, and how to examine the mental conditions of workers all depended on the knowledge of Iranian techno-scientific elites.