The new zone will run from Henry Street in the town to roughly between the Black Creek Road and Back Sandy Gully Road intersections, about 3.6 kilometres down the highway.

Adelong resident Julie Neyland said she supported changing the limit but worried that the new speed limit would clash with overtaking lanes and semi-trailer traffic.

"That road is quite narrow; I know they have taken a lot of trees out and they have given us warning about the speed changes," she said.

"But it should still be 100 km/h so you can overtake using the overtaking lane going up the hill.

"You can't have 80 km/h going up a hill and an overtaking lane as the trucks are already doing 80 because they're loaded and you can't go 100 to overtake them. It doesn't make sense."

Wagga-based MLC Wes Fang said Transport for NSW had carried out a review of the speed zone which recommended lowering the limit to improve safety for motorists.

"The review assessed a number of factors including crash history, road use, development and commercial activity in the area, traffic volumes, and property access points," Mr Fang said.

"The recommendation from this review is to lower the 100 km/h speed zone on Snowy Mountains Highway at Adelong to 80 km/h, from about 200 metres west of Henry Street to 1.7 kilometres north of Back Creek Road, a distance of about 3.6 kilometres.

"The new speed limit will provide a safer road environment for all road users with a minimal increase to travel times."

The new speed limit signs will be installed today and on Thursday.

Signs will also be in place to advise motorists of the changed traffic conditions.

Road users have been asked to keep an eye out for the changes and follow the directions of signs.