Work on Wombeyan Caves Road at Bullio is now underway.
It's taking place one kilometre east of Bullio Tunnel to Bullio Trig Station Road on weekdays between 7 am and 5 pm on weekdays.
It should be completed in 12 months time.
A reduced speed limit of 40 kilometres is in place aswell as stop slow traffic control.
IMAGE CREDIT: Wingecarribee Council