Seven cars carrying highly flammable hydrocarbons tipped over September 2013, although none spilled and no injuries were reported.
The safety board says in a report that the derailment occurred when the lip of a train wheel overloaded a switch point on the track in a rail yard.
About 140 houses in southeast Calgary were briefly evacuated.
Canadian Pacific Railway has since redesigned and improved that section of track.
The accident occurred about three months after another derailment on a bridge in downtown Calgary days after heavy flooding.
That derailment caused Mayor Naheed Nenshi (nah-HEHD' NEHN'-shee) to demand answers from the rail carrier.Suggest a correction