 Semaphore signals were replaced by standard colour light signals and ATP was fitted on the line and trains.Speed limits were increased to 75 mph (only 75 due to running on London Underground track between Harrow and Amersham), all remaining fast loops at stations were removed and the line between and Aynho Junction was singled.Stations were refurbished and even reconstructed (£10 million spent on stations alone), and signal boxes and the freight depots/sidings were demolished.