Along a mountainous stretch of Peruvian highway, the anthropologists Penny Harvey and Hannah Knox recount a conversation between highway engineers and their hotel caretaker that illustrates a needed shift in direction for the ethnography of roads and other infrastructures of transportation. In Roads: An Anthropology of Infrastructure and Expertise, the two anthropologists convey the hotel caretaker’s concern that inexplicable and uncontrollable forces govern local mountains and sometimes claim the lives of drivers crossing high passes. “Even this house is haunted by ghosts,” she tells the engineers, who are staying with her as they conduct surveys to upgrade the highway. Are they aware of these forces, she wants to know, and do they believe in ghosts? The engineers laugh, and one speaks for the others when he says that no, he doesn’t believe in ghosts, but he does believe in mathematics.