This first phase of modernisation of the line linking Besançon to the Chaux-de-Fonds aims to restore the original speed of the line in France and to maintain it in the short term by regenerating 29 linear km of tracks and strengthening around thirty works of art. In Switzerland, the railway tunnel of the Col-Des-Roches is permanently restored. The main work carried out jointly in France and Switzerland under complete line cut-off from Besançon to Locle will take place in 2021 for 8 months.