Initially the only double track was between Inverness and Dalcross and also Stanley Junction and Perth. In the 1890s the single line working was improved with the replacement of telegraphing orders to trains along the line with staff and tablet control instruments. This was later upgraded to automatic token-exchange apparatus. However, the main improvement came with the doubling of sections of line, beginning with Blair Atholl to Dalnacardoch () in 1900, extended to Druimuachdar () in 1901 and Dalwhinnie () in 1909.