It's so cold in Chicago they're lighting train tracks on fire

The polar vortex has brought about unprecedented cold conditions to the United States.

It’s so severe that workers for Chicago’s commuter rail system are going to extreme measures to keep the city’s trains running in historic cold temperatures.

Metra workers have been setting the train tracks on fire, after temperatures dipped as low as -19 degree Fahrenheit (-28 degree Celsisus) -- breaking the city’s previous cold weather record for that day set in 1966.

But, don’t be surprised. Spokesman for Metra rail was quoted telling CNN that the tracks aren’t literally being set on fire. In fact, the flames come from gas-fed heaters that run alongside the rails and keep them warm.

WATCH: How Chicago is keeping its tracks working

Video: Courtesy Metra rail

The conditions are so severe in Chicago that Chicago Mayor Rahm Emanuel described the situation as being a public health risk. “They are life-threatening conditions and temperatures,” he said.

Emanuel also urged residents to “please avoid the outdoors. If you have to go out, dress in multiple layers. Cover your nose and mouth to protect your lungs from the cold. Call 311 to locate a warming center.”