In 1944, the railway was merged to form the Chemins de fer du Jura (CJ), which converted the line to metre gauge and electrified it at 1500 Volt DC.

The main lines, which were formed quite early in the Jura were built primarily to connect to France and did not serve the Franches-Montagnes.

However, the RSG was built to standard gauge to simplify the operation of its extensive livestock and timber traffic.

On 1 July 1910, the RSG formed a joint venture with the standard gauge Régional Porrentruy–Bonfol (RPB).

The merger of the RSG with the Saignelégier–La Chaux-de-Fonds Railway (SC), the Tavannes–Noirmont Railway (Chemin de fer Tavannes–Noirmont, CTN) and the Régional Porrentruy–Bonfol (RPB) to form the Chemins de fer du Jura, which was completed on 1 January 1944, created the basis for a radical renewal of the line.

A train travelling from Saignelégier to Glovelier ran into the rubble and derailed, injuring twelve people.

The transhipment of containers carrying garbage from trucks to trains was moved from the street to the area of the former freight shed.

[3][7] The Marché-Concours national de chevaux horse race takes place in Saignelégier in August.

[12] Because the CJ is electrified at 1500 Volt DC and the SBB at 15 kV AC, multi-system equipment would be required.

After the exit from Saignelégier station the line runs down a gentle slope to Le Bémont and on to the halt of Pré-Petitjean (formerly Montfaucon), where the depot of the La Traction heritage railway is located.

The line runs on a 2.5% slope past the small lake of Plain de Saigne to the halt of La Combe (formerly Lajoux station).

Running along the rocky abyss of Combe-Tabeillon, the line passes through several short tunnels and the former halts of Sceut and Le Fondeval (formerly Saint-Brais).

The line takes a long right turn to reach the local station, where it is possible to transfer to SBB services to continue to Delémont or Porrentruy.

Ed 3/4 1, which was the only one to receive a superheater (in 1939), was also sold to Sulzer after the regauging of the Saignelégier–Glovelier line at the end of 1952 and was used at the Winterthur works.

When running in reverse, the driver had to watch the track from the rear platform; he could use a whistle and an emergency brake.