Route Selection at Usui Pass on the Ancient Tosando Road

Abstract

This study examines route selection behavior among travelers using historical mountain transport routes, focusing on the Usui Pass along the ancient Tosando route as a case study. Previous research has proposed two possible routes over the Usui Pass: the Usui Pass Old Road and the Iriyama Road. From the medieval period onward, the Usui Pass Old Road was predominantly used. Why, then, was the Usui Pass Old Road—despite its high elevation and perceived disadvantage for walking—selected as the primary route? This study investigates this question by analyzing energy consumption related to road topography and terrain steepness. The analysis of both routes revealed that while there was no significant difference in energy consumption—defined as the physical burden on the body—the steepness of the terrain made the Iriyama Road particularly hazardous. It is therefore likely that the Usui Pass Old Road was chosen for its relatively safer passage. The findings of this study suggest that long-term route selection by ordinary travelers through mountainous areas was based on rational decisions, particularly considerations of terrain. This conclusion is further supported by an examination of the historical context surrounding the routes that crossed the Usui Pass.