Merstham Quarry Tunnel
The sharing of the main line caused a great deal of friction between the SER and the London Brighton and South Coast Railway (LB&SCR), the successor of the L&BR, throughout the nineteenth century.
Eventually the LB&SCR gained Parliamentary approval to build its own independent line between Coulsdon North and Earlswood which bypassed the SER stations of Coulsdon South, Merstham and Redhill.
This involved the construction of a second tunnel to the east of the original, but 25 feet (7.6 metres) above the level of the original Merstham Tunnel. Since both routes form part of the Brighton Main Line, in order to differentiate them the former was called the Redhill Line, whilst the new line became known as the Quarry Line.
Quarry Tunnel is 2,113 yards in length and was built between 1896 and its opening on 8 November 1899. The contractor for the new work was Joseph Firbank, and the estimated cost of the tunnel was £85,000. The new tunnel was also approached by a 100 ft deep cutting on the north side