The above seems to have resulted from the uneven distribution of passengers, depending on sections as well as the policy, which has been adopted by former Japan National Railway and West Japan Railway Company since the Sanyo Shinkansen came into operation; and of strengthening the lines directly connecting cities along the Sanin Main Line and those along the Sanyo Shinkansen (In-Yo connecting line).
区間によって乗客の流動に大きな偏りがあることや、旧日本国有鉄道や西日本旅客鉄道が、山陽新幹線開業以降、山陰本線沿いの各都市から直接山陽新幹線に至る路線（陰陽連絡線）を強化してきた結果と思われる。