Traffic Congestion and Accident Externality: A Japan-U.S. Comparison

We measure the accident externality from driving in the spirit of Edlin and Karaca-Mandic (2006). We collect data that parallel those used in Edlin and Karaca-Mandic and apply their empirical method to gain further insights about the accident externality. Consistent with Edlin and Karaca-Mandic, we find larger external costs for higher density roads, although the sizes largely depend on the variable definition and the model specification. One intriguing result is that per-vehicle external costs are considerably smaller in Japan than those in the U.S. In Kyoto, for example, an additional driver increases accident costs for other drivers by $248--$802, while it is $1,725--$2,432 in California where the traffic density is approximately the same. However, on a per-mile basis, much closer externalities are obtained. This finding indicates that the large externality in high-density roads underscored in Edlin and Karaca-Mandic is partly attributed to the fact that U.S. drivers drive longer distances, comparatively speaking.