The South Wales Division was one of the three operating divisions of the Western Region. The division included the South Wales Main Line from Severn Tunnel Junction to Fishguard Harbour, as well as numerous branches in the Valleys and West Wales. The division also controlled the Central Wales Line and the North and West route via Hereford as far as the regional border at Craven Arms.The South Wales Main Line was very busy, particularly the four-track section between Severn Tunnel Junction and Cardiff, and saw InterCity HSTs and loco-hauled services to Cardiff and Swansea. DMUs were used on local services in the Cardiff Valleys and in West Wales.Freight traffic was very important on the division. Steel traffic moved between the various BSC works, and petroleum trains were dispatched from refineries at Milford Haven. Meanwhile coal was forwarded from numerous collieries, many on branches that were still controlled by semaphore signalling.