Timing is crucial in applying salt. There are two complementary strategies: anti-icing before an accumulation in order to prevent bonding of snow or ice to the pavement and deicing where salt is spread as soon after a storm actually begins to penetrate the bonded, frozen precipitation, quickly produce a brine or keep snow mealy, and allow for efficient plowing. The melting action of salt applied early in a storm works from the pavement surface up so snow and ice do not form hardpack.

There are times and storm conditions where a deicing chemical like salt is the only answer to keeping the pavements clear. For example, freezing rain cannot be plowed and chemical deicing is the only solution for clearing the roads when it occurs.

Anti-icing, applying salt before the storm actually begins is practiced in European countries and by a growing number of agencies in North America. It is being actively promoted by the Federal Highway Administration and professional snowfighters should evaluate its place in their snowfighting plans. Since Mother Nature and storm forecasting are not always precise, anti-icing strategies usually require close monitoring. But, done successfully, anti-icing is the best means to prevent ice-pavement bonding. It may be necessary to switch to conventional deicing as the storm progresses.

There are no easy answers with snow and ice control because there are too many variables. It has been estimated there are over 66,666 different storm conditions - pavement temperature, ambient temperature, pavement type, solar radiation, traffic volume, traffic speed, wind direction and velocity, type of precipitation, topography, lake or ocean effect, shaded areas (by mountains, trees or buildings) and wind chill factor, to name a few variables.

Snow and ice control is a very complex issue and those people on the front line need the best information possible so they can use their professional judgment to implement a customized strategy for each storm.

Salt is usually applied at the rate of 300 to 800 pounds per two-lane mile. As temperatures drop, either the quantity of salt or the frequency of application must be increased.

Ideally, with any deicer, at the end of the storm all applied material should be completely used. Since storm forecasting is not precise, some residue may remain on the surface after some storms. That residue, if not blown off or washed away, will be effective in helping prevent bonding of ice and snow in the next storm. A deicer only has residual effect if too much was applied for the storm condition.

Prewetting of salt. Many agencies in the North American snowbelt have found that prewetting salt with a 23 percent solution of liquid sodium chloride, a 32 percent solution of liquid calcium chloride or a 32 percent solution of magnesium chloride speeds the reaction time of salt and also provides melting action at somewhat lower temperatures. This provides a higher level of service at all temperatures. Prewet salt goes into solution faster, speeding its friction-recovering mission. And prewet salt also sticks better to the roadway surface so that more stays in the travel lanes rather than bouncing off where its ability to enhance safe driving is lost. This icreased efficiency means prewetting may actually decrease the quantity of salt required.

There are four methods of applying liquids.

• On-board where the liquid is in a tank on the spreader and dispensed as the salt leaves the spreader
• Applied to each loader-bucket of salt just prior to placing salt in spreader
• Applied to entire load of salt in the spreader
• Applied to entire salt stockpile prior to winter season.

Many agencies are selecting on-board prewetting due to its improved application and control. Prewetting is usually done at rates of 8 to 10 gallons of liquid for each ton of salt.

Spreading can be done full-width or windrow. Both have strengths depending on conditions. Pay special attention to spinner speeds. A spinner that revolves too fast will throw salt over a wide area, possibly wasting material. You may correct "overthrow" by adjusting the drop location on the spinner by using your directional baffles or reducing spinner speed. Traffic density and highway design largely determine the spreading pattern required.

A windrow of salt applied in a 4-8 foot strip along the centerline is effective on two-lane pavements with a low to medium traffic count. Less salt is wasted with this pattern and quickly gives vehicles clear pavement under at least two wheels. Traffic will soon move some salt off the centerline and the salt brine will move toward both shoulders for added melting across the entire road width.

The full-width spreading pattern is often used on multiple-lane pavements with medium to high traffic volumes. Melting action is obtained over the full pavement width. Vehicles tend to stay in line to clear wheel paths in the lanes. Often the full width pattern is used when trying to get salt down "under a storm." But be careful not to waste salt when using this pattern.

Play the wind in spreading. A strong wind blowing across a street or highway can cause salt to "drift" as it comes out of the spreader, pushing it onto the shoulder or into a gutter. This is particularly true in rural areas where there are few "windbreaks." How the wind affects spreading depends on both wind velocity and pavement condition. Spreader operators should "play the wind" to put salt where it will do the most good. As mentioned, prewetting can be used to advantage in this regard.

Give salt time to work. Time plowing operations to allow maximum melting by salt. When you plow salt off the pavement, you waste the deicing material and increase the cost of snow removal.

Know when to plow and reapply salt. The need for another salt application can be determined using "high tech" or "high touch" methods. Some agencies have installed pavement sensors which record conductivity and, hence, the concentration of chlorides remaining on the pavement. Operators can watch melting snow kicked out behind vehicle tires. If the slush is soft and "fans" out like water, the salt is still working; once the slush begins to stiffen and is thrown directly to the rear of vehicle tires, it is time to plow and spread more salt.

Has the weather changed? Remember that salt application rates may have to be increased when pavement temperatures are lower, such as at night and on sunless days. Without the sun, the effect of solar radiation and warmth is lost. Pavement temperature is rarely the same as air temperature.

Don't overlook salt's anti-skid value. For years, maintenance people have observed that salt, applied as an ice melter, also gives anti-skid protection. Tests conducted in cooperation with the National Safety Council show that salt, applied at normal deicing rates, gives as much anti-skid protection as abrasives. The anti-skid effect of salt is immediate as it starts melting snow or ice.

Safeguard the environment. The way salt is spread can make the difference between whether the public appreciates or condemns snowfighters' efforts. Overuse and misuse ignore concern for the environment. Proper calibration of spreading equipment, appropriate application and good storage can avoid most problems.