The rails and signalling have been upgraded over the years, and many sections of the line have been deviated: The original 1870s Vogel Era track had rails of 40 lb/yd (19.9 kg/m), some were iron not steel; later rails were 53 lb/yd (26.3 kg/m); and from 1901 70 lb/yd (34.8 kg/m), e.g. between Taumarunui and Taihape for the heavy X-class locos used on the central mountainous section from 1908. Some 10 bridges between Frankton and Taumarunui had to be strengthened, and in 1914 there was still 129 km (80 mi) of 53 lb/yd rail to be replaced. In the 1930s 85 lb/yd (42.2 kg/m) was adopted, then 91 lb/yd (45.1 kg/m), and from 1974 100 lb/yd (50 kg/m).