An unusually harsh winter is one of the reasons Canadian National Rail Co suffered a sharp increase in the number of train accidents in 2014, a top official said on Tuesday. Chief Operating Officer Jim Vena told a committee of federal legislators that deep cold can cause rails and wheels to crack. The company has increased inspections of tracks, he added. Canada’s safety watchdog is probing two recent accidents involving CN Rail oil trains that came off the tracks and caught fire near the small northern Ontario town of Gogama. Vena said CN Rail has imposed speed restrictions on northern Ontario tracks until it understands the reason for the derailments. A Reuters analysis this week showed CN Rail’s safety record deteriorated sharply in 2014, reversing years of improvements. The rapid rise in the transport of crude oil by rail has increased the chances of deadly derailments. A runaway oil train leveled the center of the Quebec town of Lac-Megantic in July 2013, killing 47 people.