One man is dead after a head-on collision between two bicyclists on the Jacques Cartier Bridge.

The crash happened around 4 a.m. on the bike path that runs along the western side of the bridge links Montreal to Longueuil.

The two people were bicycling in opposite directions when they smashed into each other.

A 55-year-old man died at the scene, while the woman, 24, suffered serious injuries including broken bones. The woman's life is not in danger.

Neither was wearing a helmet.

The Sureté du Quebec closed the bicycle path and a lane of car traffic while they conducted their investigation, reopening the bridge around 7 a.m. 

Police are investigating to try and determine what caused the crash. Possible causes include fatigue or a sudden swerve by one of the cyclists. 

According to Velo Quebec, fatal head-on collisions are very unusual. When they do happen, they often happen at night.

“A person dying in a collision between two cyclists, it's only the third time in my career that I’ve heard about that,” said Velo Quebec research director Marc Jolicoeur.

At night, bike reflectors are essential, but overall, the bridge's bike path is secure, said Jolicoeur.

“It is relatively safe as long as people are not going too fast,” he said.

The Jacques Cartier and Champlain Bridges Incorporated said speed reducing measures are installed on the path.

As for helmets, Velo Quebec supports their use, but cautions the helmets shouldn't give cyclists a false sense of security.