Work started in the Bradford to Thornton line on 21 March 1874. The earthworks were heavy, and construction was slow. The first section to be opened was from the St Dunstan's junctions at Bradford as far as Great Horton on 4 December 1876. The short branch line to City Road goods depot opened on the same day; both openings were for goods traffic only. The short extension to Clayton followed on 9 July 1877 or on 9 August 1877. The next stage was dependent on completion of Clayton Tunnel and Thornton Viaduct; opening for goods from Clayton to Thornton was on 1 May 1878. The line was opened throughout from Bradford to Thornton to all traffic on 14 October 1878.