As the polar vortex blankets the Chicago area with life-threatening cold temperatures this week, rail crews are literally turning up the heat in order to keep trains running.

Chicago commuter railroad Metra is using a system that runs along rail tracks to generate flames and heat to prevent rail and switch defects from the extreme cold that could halt train service.

"Pull-aparts are rail defects in which two rails separate at their connection," the railroad recently said in an Instagram post. "They occur in extreme cold when the metal shrinks and the rails literally pull apart from each other."

Once the metal is warmed up and expands, crews can then reconnect the separated rails, according to Metra.

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While it may appear to passengers on a train and in photos that the rails are on fire, Metra says that's not actually the case.

"Despite popular belief, the tracks themselves are not on fire," the agency said in a news release. "Instead, the flames come from a gas-fed system that runs adjacent to the rail, generating heat on the critical areas where the switches are supposed to make contact."

Metra uses the system to help keep switches clear and from defaulting to “fail-safe” mode, which Metra explains is when switches fail to make contact with the rail and complete an electric circuit. That halts all train traffic through the area.

"Winter weather will always be a challenge for the railroad, and though no railroad is free of switch issues, innovations like the switch heaters at A-2 help alleviate some of those obstacles," the railroad explains.

The practice isn't just used during extreme arctic weather events, but anytime the temperature dips near zero.

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In Chicago, temperatures were still dropping after plunging early Wednesday to minus 19 degrees, breaking the day's previous record low set in 1966, though wind chills in northern Illinois made it feel as cold as negative 57 degrees.

About 1,300 of Wednesday's canceled flights in Chicago were at O'Hare International Airport, one of the nation's busiest. Governors in Illinois, Wisconsin and Michigan declared emergencies as the worst of the cold threatened on Wednesday.

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At least six deaths were linked to the weather system Tuesday, including a man struck and killed by a snow plow in the Chicago area, a young couple whose SUV struck another on a snowy road in northern Indiana, and a Milwaukee man found frozen to death in a garage. Two other people were found frozen to death in Michigan.

The Associated Press contributed to this report.