Here's why trees along the M1 at West Wollongong are gone

The section has been left bare, with wooden yellow and black barriers left in their place.

The work is part of a project to erect four kilometres of safety barriers installed between Mount Keira and Masters roads.

While much of the trees and vegetation along the median will remain in place once the guardrails have been installed, a section of trees just south of the Mt Keira Road overpass have been removed.

This is because the median in that location is too small to safely install the barriers with the trees remaining in place.

"To allow for a safe deflection zone behind the guardrail and for open drainage, we are removing a section of soil mounds and trees in the median," a Transport for NSW spokesperson said.

"About 50 trees will be removed along a 200-metre stretch near Mount Keira where the guardrail is being installed."

The spokesperson said more than 70,000 motorists use the stretch of road every day.

"This stretch of road has a poor crash history, with 16 crashes recorded in the five years to July 2021. Of these, there was one fatality and a further six serious injuries," a Transport for NSW spokesperson said.

"The new flexi barriers will increase the safety of motorists by reducing the likelihood and severity of run-off road crashes and creating a more forgiving roadside environment."

The work began on March 3 and will take place for six weeks; all work will be carried out at night, between 8pm and 5am.

No work will take place on Friday and Saturday nights.

For those travelling past the work site at night, single lane closures and a reduced speed of 40km/h are in place.