Although the rest of the branch was electrified by London Underground before operations were taken over from British Railways, trains on the section north of Epping continued to be hauled by steam locomotives as a separate shuttle service. The service was operated by British Railways for the Underground until 18 November 1957, when the line was electrified and electric trains took over from steam. The low power supply prevented the Epping to Ongar section being fully integrated into the line and it continued to operate as a shuttle service.