Jalopnik explains that when temperatures are below zero, "the metal of the train tracks can contract to the point that it will pull up the bolts holding it in place," and so crews will actually burn the tracks using kerosene to warm them up. Once they've been heated, the tracks will "be re-bolted, or welding repairs can be affected on the broken tracks."
Parts of Chicago are being hit with wind chills as low as 49 degrees below zero, per The Chicago Tribune. The temperature is likely to dip below 27 degrees below zero, which would make Jan. 30 the coldest day ever recorded in Chicago's history. Brendan Morrow