After a series of tragic collisions in recent weeks, the Ontario Provincial Police are warning drivers to be extra cautious when driving during the winter.

Seven teenagers, between 17 and 19-years-old, were killed in two separate collisions that happened less than four hours apart on Tuesday.

Three of the teens were from Renfrew, Ont. Keegan Melville, 18, Zabrina Rekowski, 19, and Hillary Afelski died on Highway 17 on their way back to university in Sudbury after the Christmas holidays.

Both of the crashes were related to winter driving conditions. Police call them "avoidable tragedies."

"It is critical that motorists adjust their driving behaviour to the weather conditions, which can change rapidly and without warning," said Larry Beechey, provincial commander of traffic safety. "Even on a sunny day, black ice is a constant danger and drivers should always assume its presence."

OPP officers say it's important for drivers to constantly adjust their driving because weather can change quickly during the winter months.

They're also asking parents to speak with their children about the dangers of winter driving.

"Far too many people are continuing to take risks and are paying the ultimate sacrifice," said Don Bell, commander of the OPP Highway Safety Division. "Together we can teach drivers of all ages to become not just good drivers but good road users."

With a report from CTV Ottawa's Vanessa Lee