Heavy coal traffic used the Cannock Extension Canal for its entire life, although subsidence caused by the mining was a regular problem. In an effort to combat the effects of a section of canal sinking, the BCN erected a number of safety gates. Those at Northwood consisted of two sets of mitred gates beneath a bridge, one facing each way, so that if the canal breached, the movement of water would cause one set of gates to close, depending on which side of the bridge the breach occurred.