Waterloo Regional Police, are investigating a fatal head-on collision in Woolwich Township.

The crash happened about 500 meters from the Sawmill Road and Arthur Street roundabout near St Jacobs.

Police say shortly after 11:00 am a 74-year-old woman, collided with a transport truck after her Lexus SUV crossed over the centre line.

Staff Sergeant Jim Strand with Waterloo Regional Police Service said officers are in the preliminary stage of their investigation.

"From what we can figure out the SUV crossed over the line and was struck by the truck going in the opposite direction," says Strand.

The 58-year-old driver of the transport truck was not hurt. A third vehicle was involved in the crash but the driver only had minor injuries.

Police don't know why she crossed the line but say she was travelling southbound and clipped the mirror of a northbound SUV Before crashing with the delivery truck.