Officers issued a "major red defect notice" for the tipper truck for defective brakes on Thursday, after inspecting the trucking company's entire fleet.

A 47-year-old woman died when her motorbike and the truck crashed on the motorway at Homebush West about 1.40pm on Wednesday.

Police and paramedics treated the woman for critical injuries at the scene, near the Homebush Bay Drive exit, but she died before she could be taken to hospital.

Witnesses who stopped to give first aid told police the woman had been run over. She was treated near the wheels of the truck's rear trailer.

The 42-year-old truck driver was not injured and was taken to hospital for mandatory post-crash testing of blood and urine.

It is not yet known what caused the crash. Police from the Metropolitan Crash Investigation Unit continue to investigate.

On Thursday, police, the Environment Protection Authority, and Roads and Maritime Services inspected eight truck and trailer combinations owned by the company involved in Wednesday's crash. Police have issued defects on "a number" of the trucks for issues including worn tyres, defective brakes and worn suspension.

"Officers also issued three infringements to the owner for permitting defectives trucks to be driven," police said in a statement.

"Police will allege the truck involved in the crash on the M4 was one of the trucks inspected and was issued a major red defect notice for defective brakes."

Superintendent Stuart Smith from the Traffic and Highway Patrol Command the woman's death was tragic and highlights the risks faced by everyone on the road.

"While the investigation into this matter is ongoing, our focus is to ensure that those involved in operating, loading, or driving truck and dog trailers on our roads, are doing so safely," Superintendent Smith said.

"In this instance we have inspected a small fleet, finding worn tyres and shock absorbers, faulty brakes, air leaks, and other defects, which is unacceptable.

"This outcome should highlight the need for those involved in various projects throughout NSW, to ensure all of their trucks are safe and fully compliant, and that their drivers are fit to operate them."

Superintendent Smith said every driver, rider, cyclist and pedestrian needs to consider how they use roads in order to make it home safely.

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