Japan's topographical features permitted more gradual curves than in Norway, perhaps explaining why the 3'6 gauge was chosen over other even narrower gauges. Edmund Morel (1841–71), a British engineer hired by the Japanese government, conferred with Inoue and it is likely that these two men agreed on 3'6.

Most of Japan's conventional rail network (excluding the Shinkansen) uses 3' 6" (1,067 mm) narrow gauge primarily due to historical economic and geographic factors from the late 19th century. When Japan began building its first railway between Tokyo and Yokohama in the 1870s, they sought advice from British engineers. At the time, narrow gauge was favored because it was cheaper and faster to construct in mountainous terrain, as it allowed for sharper curves and narrower tunnels, which reduced the need for massive earthworks and expensive bridges. This was particularly important for a nation with a developing economy and a rugged landscape. While this gauge served the country well for decades, its limitations became clear as the population grew; narrow-gauge trains are generally slower and have lower stability at high speeds compared to "standard gauge" (4' 8.5"). When Japan developed the high-speed Shinkansen (bullet trains) in the 1960s, they realized they had to build entirely new, dedicated tracks using standard gauge to achieve speeds of 200+ km/h. Today, Japan maintains a dual-gauge system where the "legacy" narrow-gauge lines handle regional and local traffic, while the standard-gauge Shinkansen handles the high-speed intercity routes.