In order to maintain open highways and increase highway safety, the northern tier of the United States has used salt (sodium chloride) for years to combat ice, snow and sleet. Over the last decade, many state highway departments have switched to the more effective calcium chloride (CaCl2) and magnesium chloride (MgCl2) deicers because they provide lower freeze points, are less expensive, less corrosive to concrete and less harmful to the environment. However, the use of these additional road salts has resulted in a major increase in vehicle corrosion, particularly the underbody and electronics of buses and other fleet vehicles.

The sodium, calcium and magnesium chloride salts lower freeze points of water to keep highway surfaces wet and slushy rather than icy. Magnesium and calcium chloride are much more effective deicers because they stay liquid at a much lower temperature and less material is required to melt the same amount of snow and ice. Many state DOTs are now spraying calcium and magnesium chloride solutions on the roads prior to and after winter storms. These deicers are often mixed with sugar beet juice or vegetable oils for better adhesion to the road surface. While the roads are safer, the deicer cocktail, sand and traditional road grime create more difficult vehicle cleaning conditions.

While these antifreeze salts are water soluble for deicing applications, the calcium and magnesium chlorides get quite viscous as water evaporates, collecting sand and dirt and form compacted deposits in recessed areas. These difficult-to-remove deposits are the source of major chloride corrosion. To complicate the situation further, if the road salts are not removed from the vehicle, MgCl2 and CaCl2 will pull moisture out of the atmosphere, rewet and continue their corrosive actions.