Police believe a driver may have had a coughing fit before veering onto the wrong side of the road and colliding head-on with an oncoming vehicle.
The driver of the Holden Commodore sedan was taken to Dandenong Hospital with serious, but non life threatening injuries following the two car collision in Princes Way, Drouin last Tuesday.
The collision occurred at about 5.30pm. Police said the Holden, driven by a 68-year-old Drouin man, was travelling west at an estimated speed of 70 kilometres/hour.
Police said the vehicle veered onto the wrong side of the road, colliding with a Toyota Prado travelling east and driven by a 67-year-old Bunyip man.
Two passengers in the Toyota Prado, aged 14 and 15-years-old, also of Bunyip, were taken to Dandenong Hospital for observation.
Both vehicles sustained extensive damage.
Police are continuing investigations in the collision.