The Taff Vale Railway working with the Cardiff Docks, and later the Rhymney Railway, also to Cardiff Docks, proved immensely successful. However volumes of traffic, most especially coal for export, increased hugely as more collieries, and more efficient methods of winning coal, were operative. Cardiff Docks were seen as a near-monopoly, and as such were thought to be unresponsive to customers' wishes. Coal ships intending to load at Cardiff were often obliged to stand off for days waiting for a berth, and loaded coal trains heading for the docks frequently were obliged to wait in loops and on goods lines on the approach, waiting for clearance to enter.