Provincial police say they're putting transport truck drivers "on notice" after laying charges in three horrific collisions involving big rigs that claimed the lives of six people.

OPP Commissioner Vince Hawkes says two of the collisions occurred on Highway 401, one near Port Hope, Ont., on Aug. 3, and the other in Chatham-Kent, Ont., on July 30. The third occurred on Highway 48 in Georgina, Ont., on July 27.

Hawkes says two people were killed in each of the collisions in which it's alleged a transport truck crashed into traffic that was stopped or had slowed down due to road construction or a collision.

The four men, one woman and 14-year-old boy who were killed in the crashes were all occupants in vehicles at the end of the traffic queues.

Hawkes says the details mirror a fourth collision on May 11 on Highway 401 near Kingston, Ont., in which three men and a woman died when their vehicle was struck from behind by a transport truck in a construction zone. Charges have already been laid in that incident.

Hawkes says the OPP is "putting drivers on notice" that it will pursue every investigative avenue to hold at-fault drivers accountable to the full extent of the law.