Gradients on the main line from Llanelli to Llandilo were significant, climbing at 1 in 157 to 1 in 108 for several miles to a summit at Derwydd Road, then falling at 1 in 108 for two miles to Ffairfach.
The Pontardulais to Swansea line was undulating with stiff alternating gradients; Dunvant was approached by miles at 1 in 72 eastbound and two miles at 1 in 70 and 1 in 80 westbound.