Dublin and Drogheda Railway (D&D) was a railway company in Ireland which publicly opened its 31¾ mile main line between Dublin and Drogheda in May 1844. It was the third railway company in Ireland to operate passenger trains and the first to use the Irish standard5 ft 3 in (1,600 mm) gauge. It later opened branches to Howth and Oldcastle. The opening of the Dublin and Belfast Junction Railway (D&BJct) between the D&D at Drogheda and the Ulster Railway (UR) at Portadown in 1852 saw an almost continuous main line connection between Dublin and Belfast, which was resolved by the official opening of the Boyne Viaduct in April 1855. Amalgamations between these and other companies in 1875 and 1876 saw the creation of the Great Northern Railway of Ireland GNR(I).
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