It's expected to take a year to investigate a near-collision on January 2 between two trains - one of them - bound for Colac and Warrnambool.
The Australian Transport Safety Bureau says an empty train travelling from Waurn Ponds to Geelong went through two stop signals at Marshall and was in the path of a passenger train going the other way from Melbourne to Warrnambool.
Both trains stopped 300 metres short of a head-on collision.
Public Transport Users Association Geelong convenor Paul Westcott says fortunately both train drivers saw each other.
"It obviously is a concern if, in this case, a train going to Geelong from Marshall went past a red signal for reasons that obviously are subject of the investigation and was on the same track and heading in the opposite direction to the Warrnambool train.
Liberal South Barwon MP Andrew Katos says it highlights the need for the duplication of the track.
"Daniel Andrews is spending billions and billions of dollars on rail infrastructure in Melbourne but none of that money is flowing out into regional Victoria and this highlights the absolute need for the duplication of track between South Geelong and Waurn Ponds stations.