The three Newtyle lines had been conceived to carry materials and passengers between Dundee and Strathmore. The Coupar Angus and Glamis lines were now part of the through main line between Perth and Aberdeen, and the importance of traffic to and from Dundee was much reduced: Newtyle and the other locations on the line were simply small rural settlements. (Newtyle had a population of 1,139 in 1861, 883 in 1921 and 766 in 1981.) In the early years of the twentieth century, Dundee was growing in importance, and in size, and travelling to work by train was rising in significance. However, the Newtyle line made wide sweeps to reduce the gradients and the trains were slow and infrequent. When street-running passenger tramways were introduced they abstracted considerable traffic from the line, and decline set in. The Caledonian Railway, as owner of the line, was a constituent of the new London Midland and Scottish Railway under the Railways Act 1921, and the remote and eccentric backwater line was even less significant.