The Conwy Valley line between Blaenau Ffestiniog and Llandudno Junction will be closed again for upgrading after damage caused by Storm Gareth in March.
A replacement bus service will run for three weeks from Friday 22 November until Sunday 15 December.
The work includes installing 600 rock bolts in the Ffestiniog Tunnel, replacing sleepers along the line and vegetation management. The flood damaged platform at Dolgarrog station will also be repaired. It remains closed.