During severe storms, crews might have to apply more salt as they plow, usually at a rate less than the initial application. They occasionally apply salt lightly after a storm to remove residual snow and ice. Even with these supplemental applications, the overall result of pretreatment is use of far less material than required for post treatment operations. Many departments in northern states have adopted similar policies and procedures. Timing of the pretreatment is so important that managers need dependable weather forecasts.
Local judgement is often necessary where elevations differ within a city or town.
Liquid chemical applications are of two types. It should be noted that prewetted material is applied at same rate as dry salt. The most common prewetting agent is calcium chloride in the eastern U.S., and magnesium chloride in western states. A second liquid application is spraying chemical directly on the roadway. Nationally, the most common chemicals are salt brine and magnesium chloride in solution.