A section of Picton Road had its speed limit slashed on Monday.
The section of the road that runs past the Bingara Gorge residential development has seen its speed limit drop from 100km/h to 80km/h.
The speed reduction is in place between Almond Street and Pembroke Parade and was put in place after a review by Roads and Maritime Services, said Wollondilly MP Jai Rowell.
"The review was carried out in accordance with the NSW Speed Zoning Guidelines and in consultation with Wollondilly Shire Council," Mr Rowell said.
"The review assessed a number of factors including roadside development, traffic characteristics and crash profiles.
"The change will make the speed limit more consistent with the road environment and aims to improve safety for all road users."
The change is said to be the first speed reduction since the 100km/h limit was restored in September last year after Roads and Maritime Services finished an extensive series of road safety works.
The $53 million roadworks covered several sections along the stretch of road and included installing concrete medians, realigning curves, widening the road and improving drainage.
More than 100,000 man hours of work were put in to install 6.5 kilometres of new guard rails and an extra 1.5 kilometres of overtaking lanes in both directions.
The section of the road where the speed limit has changed was not where work was done.
Statistics last year showed that the works reduced the number of crashes and casualties even before they were finished.
In 2010, the first full year of the safety roadworks, the number of crashes recorded was 28. This was a decline on the previous year's figure of 36.
The number of casualties climbed by one in 2010 to 24 but had gradually fallen to 20 in 2012.
The road saw another accident on Friday, when the driver of a new truck collided with two other trucks roughly two kilometres from the Mount Ousley turn-off.
"In the nine months since the change in speed limit, preliminary crash data shows there have been 19 reported crashes compared to 155 crashes in the previous five years," an RMS spokesman said.
News speed zones in force
Another speed zone change occurred on Monday along Nerriga Road between HMAS Albatross and Nerriga.
An RMS review found the existing limits were not suitable.
They have been replaced with a 100km/h zone between HMAS Albatross and Tianjara Falls.
From Tianjara Falls to Touga Road is now 80km/h.
The bends between Touga Road and Nerriga are 60km/h before returning to 100km/h to Nerriga.