The line up from Vietnam was a political project designed to extend French influence into southern China, and to beat the British in particular to trade opportunities which were largely chimaeric. The British considered building a competitive extension from Burma and over equally difficult terrain. The southern half the run to the Vietnamese border is largely composed of tunnels, bridges, and galleries, and was extremely expensive to construct. In more than a century of operation it has frequently been damaged or blocked by landslides, and this is also given out as the reason for currently restricting the service to daytime operation only. At the time of its construction other foreigners marvelled equally at the engineering and the economic folly.