Winter weather extremes lead to an increase in potholes on state highways and bridges. Potholes form when moisture seeps into cracks in the pavement, then freezes and thaws, causing the cracks to expand. The constant pounding of traffic loosens the pavement which causes it to crumble and create potholes.Severe swings in temperature such as Tennessee has experienced over the past several days, followed by periods of rain, are the perfect conditions for widespread potholes to form.