A vehicle carrying a couple and their eight-month-old child flipped several times after being struck on the Princes Fwy at Longwarry on Saturday morning.
Police said the collision occurred on the west bound lane as traffic slowed to 40km/h for roadworks at about 11.30am.
They allege a gold Mitsubishi had been speeding and weaving through traffic before it rear ended a white Mitsubishi wagon, causing it to flip three or four times.

Police reported the gold vehicle failed to stop at the scene and trave