The driver of a pick-up truck that killed three cyclists and left three injured Friday in Rougemont was coming off a night shift and driving on cruise control, the coroner said Saturday.

Police spent Friday and Saturday investigating the shoulder of Highway 112, the scene where five women and one man from the Club de Triathlon St. Lambert were struck from behind while riding single file to a training event in Sherbrooke.

The three women killed were 36-year-old Sandra De-La-Garza-Aguilar from St. Bruno, 39-year-old Lyn Duhamel from Boucherville and 44-year-old Christine Deschamps.

The other three victims, a 57-year-old man, and two women, aged 44 and 31, are expected to survive, according the Surete du Quebec Sgt. Claude Denis.

The SQ was initially puzzled by how the crash occurred and had ruled out alcohol, but the coroner's conclusion pointed to the dangers of using cruise control while drowsy.

"They have the impression the car drives by itself, but there's always a lack of attention," said coroner Andre Dandavino, who investigated the collision.

Unsafe driving habits was just one of the factors at play, said Dandavino.

Quebec's policy is to add paved shoulders to busy roads. The shoulder on that stretch of Highway 112 is set to be paved in a few weeks, but the coroner said it should have happened long ago.

"We're asking people to do more exercises to be more environmental, but we need to give them the possibility to do things in a secure way," he said.

Though adult cyclists have the legal right to be on roads like Highway 112 under Quebec's highway code, if a path exists nearby, they are obligated to use it.

A gravel path runs parallel to Highway 112 only 50 metres away from the site of the collision, but a gravel path isn't made for road bike with thin tires, explains Dandavino.

To keep an incident like this from reoccurring, prevention campaigns are crucial, said Louis Barbeau from the Quebec Cycling Federation.

"Especially at this time of year, cyclists are coming onto the road. They're vulnerable. People have been driving on the roads without having to care about cyclists for a number of months, and all of a sudden, you have hundreds and thousands of cyclists," said Barbeau.