Between Saunderton and Princes Risborough, the Wycombe Railway single line descended steeply and had a tight curve, and the new down line was to be deviated from it somewhat to ease the gradient to a maximum of 1 in 87 and to ease the curve. The abandoned formation of the original Wycombe Railway may still be detected. Even 1 in 87 was considered to be too steep an uphill gradient for heavily-laden freight trains heading for London, so the new up line was planned to take a slightly different alignment with a deep cutting and a short tunnel, enabling a maximum rising gradient of 1 in 167.