sentences:  During construction in 1859, the C&C railway attempted to switch from broad gauge to standard gauge, which would have meant all railway infrastructure (including the tunnel), could be built to smaller (and thus cheaper) dimensions.Such a change would require the approval of the British Parliament and pressurisation on the company by the South Wales Railway, a broad gauge line in the area which did not want the rival standard gauge making an incursion on its territory, meant the application to Parliament never occurred.Digging initially proceeded from four sites - at either end and from the bottom of the first ventilation shaft sunk.