Much of Laos lacks adequate infrastructure. Laos has no railways, except a short link to connect Vientiane with Thailand over the Thai–Lao Friendship Bridge. A short portage railway, the Don Det—Don Khon narrow gauge railway was built by the French in Champasak Province but has been closed since the 1940s. In the late 1920s, work began on the Thakhek–Tan Ap railway that would have run between Thakhek, Khammouane Province and Tân Ấp Railway Station, Quảng Bình Province, Vietnam through the Mụ Giạ Pass. The scheme was aborted in the 1930s. The major roads connecting the major urban centres, in particular Route 13, have been significantly upgraded in recent years, but villages far from major roads can be reached only through unpaved roads that may not be accessible year-round.