Problems linked to uncontrolled and unplanned movements or runaway trains can be attributed to three factors. The first is a loss of control, as was the case in the Field accident. The train was attended, but for reasons yet to be determined, it derailed. The second factor is a change in car distribution in the yard. The third factor concerns unattended and improperly secured cars, as was also the case in the Lac-Mégantic incident.
Each of those factors has to be examined to determine whether the measures taken will reduce the risk of a train or some of its cars derailing, but we aren't there yet.