Before revision: It was first thought of in the late 1980s as Japan faced ever increasing land values in the economic bubble, to allow the utilization of heretofore unused deep underground for necessary water and utility ducts and other city tunnels.
After revision: It was first thought of in the late 1980s as Japan faced ever-increasing land values in the economic bubble, to allow the utilization of heretofore-unused deep underground for necessary water and utility ducts and other city tunnels.