Application of Snow and Ice Control Chemicals

Excerpted from the CLRP Workshop Manual “Snow and Ice Control” - available on our website

The application of snow and ice control materials should always be based on local policy and local level of service determinations. The goal is to produce a fairly high level of service at a modest cost. After an ice control treatment for prevailing conditions has been decided, the final step is to get the designed treatment in the right location at the right time. The following techniques can optimize treatment effectiveness. Keep in mind that application rates for various ice control chemicals will have to be adjusted to reflect the properties of the individual chemical.

Two-Lane Two-Way-Traffic Highways (One Lane Each Way)

The most effective way to treat this highway is to spread the ice control chemical in about the middle third of the highway. The slope of the highway and traffic will distribute the chemical fairly quickly across the entire pavement. When doing simultaneous plowing operations, care must be taken not to plow chemicals off too quickly. Set the spreader to spread only in the plowed path. If plowing is not anticipated, spread the entire middle third on the “out” run of an “out and return” route. It is okay to have a truck on the road not spreading if it is part of a planned strategy.

Multi-Lane Highways

Most agencies spread ice control chemicals on multi lane highways as nearly full width as possible. Care must be taken not to spread beyond the pavement limits. Narrow bands of material near the high edge of each lane are also effective.

Parking Areas and Walkways

Spreading ice control chemicals as evenly as possible over the entire paved area is recommended for parking areas and walkways. These areas present a unique opportunity for anti-icing with solid chemicals as traffic will not displace them from the surface. Caution should be used to prevent excessive applications that remain between snow and ice events.

Hills, Curves and Intersections

Because of the higher friction requirements on hills, curves and intersections, many agencies use a higher application rate than on straight sections of highway. On lower level of service highways, these are sometimes the only areas that receive treatment. When doing special treatment at intersections, it is important to carry the treatment beyond the point where traffic normally backs up in snow and ice conditions.

Bridges and Other Structures Not Resting on Earth

In the fall and at other times when there is a rapid, severe decrease in air temperature, elevated structures are likely to be colder than adjacent pavement on earth. It is appropriate to increase application rate on these structures so critical dilution will not occur or will occur at about the same time as the surrounding pavement. Toward spring, when air temperatures are warming, structure temperatures are likely to be warmer than the surrounding pavement. Higher application rates are not necessary in this situation.

Strong Crosswinds

When spreading in strong crosswinds, try to keep the spreader upwind of the intended spread location. If the wind is too strong, spreading may not be appropriate.

Banked or Elevated Curves

Try to keep the spread pattern on the high side of elevated curves. As the chemical works, chemical brine will migrate over the remainder of the pavement.

Changes in Maintenance Jurisdiction or Level of Service

Sometimes where maintenance jurisdiction or mandated level of service changes, there will be a dramatic change in the available pavement friction. This is a dangerous condition as it is usually unexpected. To alert motorists, appropriate signing or transitioning of the level-of-service treatment should be used.

Worst-Case Scenarios

The worst cases usually occur when the chemical treatment is quickly overwhelmed (diluted) by excessive amounts of water or ice. Blizzard conditions (intense snowfall, wind, very cold temperatures) quickly dilute ice control chemicals and render them virtually useless. If the pavement temperature going into and coming out of a blizzard is expected to be low, then plowing only is probably the best strategy. After the blizzard, if it is still very cold, use abrasives as necessary until warmer temperatures will allow chemical deicing to work. If the pavement temperature throughout and after the blizzard is likely to be fairly warm, a treatment with an ice control chemical before or early in the storm followed by plowing only throughout the storm, will make deicing at the end of the storm much quicker.

Rapidly accumulating freezing rain is another maintenance nightmare. The best strategy is to apply solid ice control chemicals, at a high rate, in very narrow bands in the high-side wheel path of each lane. With luck, there will be a location in each lane that will provide enough friction to allow vehicles to stop and steer. In situations where falling and/or blowing snow make visibility near zero, it is a good idea to get snow and ice control vehicles well off the road. Operating in those conditions is a risk to everyone involved.

Typical Spread Patterns for Snow and Ice Control Materials

The figure on page 7 illustrates five typical general spread patterns and their use. This should strongly suggest that identifying spreader settings to achieve these patterns should be part of the calibration process. It is likely that optimum spread patterns will change before, during, and after winter weather events as weather and operational conditions are continually changing.

Most solid ice control materials spreaders have adjustment capability that will achieve these patterns. These include:

Spinner speed

This controls how far the material is cast.

Deflectors

These limit the cast of the materials. Note: When there is deflector control, increasing spinner speed will not increase cast distance.

Drop location on spinner

The bulk of the material discharged will be about 180 degrees from the drop location.

Spinner direction

The direction of rotation can be changed by reversing the hydraulic hoses that drive the spinner motor.

Table - Discharge and Application Rates
Discharge Rate: kilograms per kilometer (pounds per mile)

Application rate per lane, by number of lanes being treated

 
1
2
3
28 (100)
28 (100)
14 (50)
9 (33)
56 (200)
56 (200)
28 (100)
19 (67)
84 (300)
84 (300)
42 (150)
28 (100)
112 (400)
112 (400)
56 (200)
37 (133)
140 (500)
140 (500)
70 (250)
47 (167)
168 (600)
168 (600)
84 (300)
56 (200)
196 (700)
196 (700)
98 (350)
65 (233)
224 (800)
224 (800)
112 (400)
75 (267)

Achieving the desired spread patterns is largely a trial and error process. They can be established by observing the accumulation of material on the floor of the chemical storage facility. They should be verified by observing the pattern during field operations.

Getting the Application Right

Application rates for ice control chemicals are usually specified in pounds-per-lane-mile or kilograms-per-lane-kilometer. Spreaders are usually calibrated to deliver pounds per mile or kilograms per kilometer (the discharge rate). It is important to understand that relationship in order to be sure the proper application rate is being used. The application rate is the number of pounds or kilograms dispensed per mile or kilometer (the discharge rate) divided by the number of lanes being treated. The table on page 6 demonstrates discharge and application rates.

Figure - Spread Patterns

Fall 2010

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This work by the Cornell Local Roads Program (CLRP) is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.