Five people have been killed in 24 hours on Victoria's roads with the latest fatality a woman who was killed when her car and a truck crashed.
The woman died after her car and a truck collided at Salisbury West on Wednesday afternoon.
Her female passenger was taken to hospital with non-life threatening injuries and the truck driver is assisting police.
Earlier the Monash Freeway was closed to city-bound traffic after a 24-year-old motorbike rider was killed as he was moving between traffic and lanes.
The rider bounced off a car while he was moving and went underneath a B-double truck, Police Assistant Commissioner Stephen Leane said on Wednesday.
"One of my own staff members was on the freeway and was passed by the motorcyclist at speed so there was an issue well before the collision," the senior officer told reporters when asked about the cause of the crash.
"We're not sure if it was lane splitting but certainly the rider took avoidance action about not hitting a car that slowed in front and as a result of that bounced off one car and went under the wheels of the B-double truck."
Mr Leane admitted there was "error involved" in the crash as investigations continued.
"He's taken a dangerous manoeuvre in high traffic, run the risk and he's lost his life," he told 3AW.
Drivers who witnessed the crash were offered trauma counselling.
Two drivers died in a fiery collision between two cars in Mannerim, south of Melbourne, just after 10.30pm on Tuesday.
"One vehicle came into an intersection at speed and didn't appear to obey any signal or give way," Mr Leane said.
"Both vehicles were catapulted into a farmer's paddock and quite extraordinarily, both caught fire.
"Had there been more than one person in each (car) we would have been talking about a serious multiple loss of life."
A third driver died in a separate crash in Castella, northeast of Melbourne, after hitting a wallaby, overcorrecting and hitting a tree.
The deaths take Victoria's 2019 road toll to 33, which is 11 higher than the same time last year.
About a third of the fatalities have been motorcyclists.
Traffic Accident Commission boss Joe Calafiore described it as a tragic start to the new year.
"We beg Victorians to ease up on the roads, to take your time and put an end to this carnage," he said.
Premier Daniel Andrews echoed the message.
"Today's event and events across the last few weeks are a timely reminder, a tragic reminder, that we have to keep on getting that message out," he said.
"We all just need to take that moment to think about being a little more sensible and that's how we save lives."
