From 1899 to 1926, production continued on a restricted basis but, during that period, technological improvements were made which meant that the lode could be economically mined.

[8] The strengthening girders came from the original viaducts over Wollondilly, Boxers and Barbers Creeks on the Main South line which had been replaced during duplication work in the 1912–14 period.

On 7 February 1939, the line was made available for traffic to a point beyond Hoskinstown, where a temporary siding and unloading facilities were provided.

The Captain's Flat line opened for general traffic on 17 June 1940 when a tri-weekly rail motor service began.

[1] The new line was 21 miles 11.25 chains (34.0 km) long and was worked under Ordinary Train Staff and Ticket conditions.

By November 1960, passenger traffic had dropped considerably, due to the improvement of the road to Queanbeyan, which was substantially shorter than travelling via Bungendore.

[10] On Sunday, 10 August 1969, the line was temporarily re-opened as the location for the railway scenes in the feature film, Ned Kelly, starring Mick Jagger.

It was understood that there was an interest in creating a walking track or a tourist railway over the last section of the line into Captain's Flat.