The Dyne Steel Incline was a steam-powered tramroad that carried tram loads of cast iron up and over the hill between the Blaenavon Ironworks and Pwll Du.

From there the trams continued along Hill's Tramroad to the Garnddyrys Forge and on to the Llanfoist wharf.

From 1817 the main route for exporting products of the Blaenavon Ironworks was northward through the Pwll Du Tunnel and then along Hill's Tramroad to Llanfoist, from where the goods were shipped by the Brecknock and Abergavenny Canal in the Usk Valley.

Around 1850 Thomas Dyne Steel (1822–98), engineer of the Blaenavon Company, designed a standard-gauge railway that ran from New Pit up the mountain and then down to Pwll Du.

A stationary steam engine and winding drum at the summit pulled the trams up both sides.