As long as there have been roads—and vehicles to travel them—municipalities have been faced with the challenge of implementing snow and ice maintenance programs. The newest “old” technologies—pre-wetting and anti-icing—have been around for some time, but not widely used. Pre-wetting is applying a liquid chemical or salt brine solution to a deicing material before spreading it. In anti-icing a brine solution is sprayed directly onto the roadway. These basic practices have considerable benefits.
Spread bulk materials tend to bounce off the roadway during application or to be swept away by wind or traffic before taking effect. Some municipalities address this by spreading much more than necessary, assuming that enough will remain to do the job. Though crudely effective, the result is wasted material and expense, not to mention the negative environmental impact.
Continued application problems eventually led to the practice of pre-wetting the spread material. The logic is if the salt is wet, it's more likely to cling to the road than bounce or blow away.
At first operators used water to saturate the materials loaded into the spreader's hopper. However, most now use a part-brine, part-water solution to prevent the load from freezing. Some still wet the material as it's loaded into the hopper, but most use equipment that sprays the brine onto the material as it hits the spreader's spinner, resulting in a more uniform application of brine.
Pre-wet deicing materials also dissolve snow/ice faster. Generally, melting depends on the agent's ability to attract sufficient moisture from the environment and then form a liquid brine. Brine, simply a mixture of water and the active deicing material, lowers the freezing point of water and begins to melt the surrounding snow/ice. Using granular deicers alone is fine—if the conditions are right. But if temperatures drop below freezing, there is usually no moisture on the road, and salt alone is ineffective. Pre-wetting the salt ensures that enough moisture will be present to facilitate melting.