News release

Worn coupler component led to July 2015 runaway, collision and derailment at CN MacMillan Yard in Toronto, Ontario

Richmond Hill, Ontario, 26 October 2017 – The Transportation Safety Board of Canada (TSB) today released its investigation report (R15T0173) into the July 2015 uncontrolled movement of 91 cars which subsequently collided with and caused the derailment of an inbound train in the Canadian National Railway (CN) MacMillan Yard in Toronto, Ontario.

On 29 July 2015, a cut of 91 cars, led by 24 tank cars loaded with petroleum crude oil, separated from a yard locomotive as it was being pulled out of a pullback track. The cut of cars rolled uncontrolled back into the receiving yard, reaching a speed of about 13 mph before it collided with inbound CN freight train 422. The head-end locomotives of train 422 were shoved back about 350 feet, resulting in the derailment of 10 of the train's cars, and one car on an adjacent track. Approximately 585 feet of track was damaged. There was no release of product and there were no injuries.

The investigation found that the cars separated when a worn component in the first car's coupler assembly only partially engaged the coupler knuckle connected to the locomotive. When it reached peak load near the top of the pullback track, the partially engaged component yielded, releasing the 91 cars. It is likely that the conductor of the remotely operated yard locomotive had not confirmed that the coupler knuckle was fully engaged before moving the cut of cars out of the receiving yard. Furthermore, the receiving yard was not equipped with any means to slow the cars, and the authorization that allowed train 422 to follow behind the assignment into the receiving yard put it in a vulnerable position once the cut of cars separated and rolled uncontrolled back into the receiving yard.

Following the occurrence, CN issued guidance to its employees on how to ensure that couplers are properly locked. Transport Canada conducted a follow-up regulatory inspection at CN's MacMillan Yard to verify compliance against data for all hard coupling events. It is also developing a tank car monitoring project with the National Research Council of Canada, which should provide a better understanding of the operating environment that tank cars and their commodities experience while in transit.

See the investigation page for more information.


The TSB is an independent agency that investigates marine, pipeline, railway and aviation transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.

For more information, contact:
Transportation Safety Board of Canada
Media Relations
Telephone: 819-994-8053
Email: media@tsb.gc.ca