Work to make the century-old Lachlan River rail bridge on Lower Bathurst Street fit for the future of Inland Rail is progressing well.

The bridge is currently behind scaffolding, with modifications taking place so it has enough height to cater for double-stacked freight trains.

As the bridge itself has just enough height for the planned new trains, the work involves removing some of the support structures that sit inside that frame and putting them outside, Malcolm Clark, Project Director for Albury to Illabo and Stockinbingal to Parkes, has explained.

The bridge is more than 100 years old - designed in 1912 and commissioned in about 1918.

"It's in line with that corridor," Mr Clark said.

"The whole rail corridor through there was done in the 1910s, early 1900s era so it's over 100 years old now."

On the whole, with some upgrades done in 1996, it's holding up well and this next work will take it into the future.

Work on the bridge is being carried out in three stages, starting at the top of the bridge and currently concentrating on the middle section.

"In the new year that scaffolding will be removed and put onto the bottom deck," Mr Clark said.

The project is actually ahead of schedule with crews commencing work that was planned for the new year.

Progress on the Forbes set of works, which also includes lowering the track at Wyndham Avenue and building a new crossing loop north of Daroobalgie road, is ahead of schedule overall, Mr Clark said.

The team had a five-day window in September where trains were not running on the tracks and this allowed them to carry out major works that will allow the double-stacked trains to go under the bridge at Wyndham Avenues.

"The track below the bridge was commissioned in September," Mr Clark said.

About 300m of track was lowered below the bridge, about 1.5m in rail height.

The site itself is now getting close to completion, with the commencement of revegetation work.

The next track possession - where there are no trains running on the line and Inland Rail can carry out the major works it cannot while the line is operational - is in March 2025.