What could have caused the freight train derailment in Repentigny?

A freight train derailment in Repentigny over the weekend sent dozens of railcars off the tracks and left many residents shaken. While investigators are still working to determine exactly what happened, some experts say the recent stretch of extreme heat may have been a contributing factor. Transportation planning expert Pierre Barrieau spoke to Ken Connors. Photo Credit: THE CANADIAN PRESS/Christopher Katsarov