A mum of four who was killed when a metal tool smashed through her windscreen in a freak accident on a Melbourne motorway has been identified.

Mary-Anne Grech, from Deer Park, was driving on the M80 Ring Road in St Albans when her vehicle was struck about 4pm Thursday.

Police say a one-metre-long metal item fell off the back of a truck, hurtled across the motorway and slammed through the front of the woman’s car.

It’s believed the deadly projectile bounced over the freeway barrier and landed in the opposite lanes.

Forty-six-year-old Grech, a married mum and grandmother to three, was the sole occupant and tragically died at the scene.

Police said the truck failed to stop and was last seen travelling in the direction of Altona.

Major Collision Investigation Unit detectives would like to speak to the truck driver and are appealing for public assistance.

Police have appealed for anyone with dash cam vision to come forward.

The riv-nail driver was one metre long by 30 centimetres wide. Photo: Victoria Police

The piece of metal is believed to be a specialised tool designed for maintaining conveyer belts known as a riv-nail driver.

It is used to install rivets to fasten metal clips onto the end of conveyor belts in industries like mining, manufacturing, and food processing.

A friend of Grech’s paid tribute to the “gorgeous pretty lady” on Facebook.

“In this accident, our friend Mary-Anne Grech has passed away so young,” she wrote.

“She was such a beautiful lady rest in peace Mary-Anne Grech.

“I can’t believe this terrible news see she was such a gorgeous pretty lady rest in peace my gorgeous girl and rest in peace to her family and friends like me.”

Detective Sergeant Mark Amos said a family would be missing their mother and grandmother this Christmas.

“We need to try and find some answers for this poor woman’s family because it’s a really sad set of events and we want to work out why it has occurred and give some answers to (the family) who are sadly going to this year’s Christmas minus one person,” he said.

Mary-Anne Grech will be missing from the family Christmas this year. Photo: Facebook

He urged drivers to secure their loads.

“We need to take greater care; if you have a load on the trailer or a truck, just secure it. If you see debris on the roads, report it.

“We have to be responsible with what we do and until we start treating the roads with some respect.

“Sadly, I fear I will be doing this for the rest of my life.”

Victoria Police major collision investigation unit detective inspector Craig McEvoy urged the driver to come forward.

“Please, if it is yourself and you have now identified through searching of your equipment and your tools that you are missing this item … please come forward and let us know so you can assist us with our inquiries,” Inspector McEvoy said.

Anyone who witnessed the incident or who has footage, is urged to contact Crime Stoppers on 1800 333 000 or visit www.crimestoppersvic.com.au