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Wisconsin's DOT says salt’s effectiveness against snow and ice declines as temperatures drop below 15-degrees. In lower temperatures, they mix salt with sand, calcium chloride or magnesium chloride to enhance effectiveness and provide additional traction.
Additionally, about 90-percent of the state's contractors pre-wet salt just before applying it to roadways. Pre-wetted salt adheres better to pavement, starts the melting process faster, and can save money by reducing overall salt usage about 25-percent compared to dry salt. Pre-wetting using a salt brine or similar liquid can also help salt work better at lower temperatures.
Plowing is still the work-horse when it comes to removing snow and ice from Wisconsin highways," said WisDOT Winter Maintenance Engineer Mike Sproul. "Salt accelerates melting, but most importantly, salt keeps snow and ice workable so it can be removed by plowing."
During sub-zero temperatures like Wisconsin has experienced this winter, the only practical snow removal technique is plowing. Prior to certain weather situations, highway crews sometimes do "anti-icing" – spraying bridge decks, curves, hills and other known trouble spots with a salt solution to prevent snow or ice from bonding to the pavement.
WisDOT oversees about 60 remote weather information stations along the state highway system that continually gather and transmit information on air and pavement temperatures, relative humidity, wind speed and direction, depth of precipitation on the roadway, and even salt concentrations. The comprehensive data helps highway departments know how and when to treat specific highways.