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15 CHAPTER 7 RECOMMENDED SNOW AND ICE CONTROL PRACTICES The goal of effective snow and ice control programs should be to provide the highest LOS possible within the constraints of available resources and environmental responsi- bility. LOS goals are viewed from the time frames of within- winter weather event and after-end-of-winter weather event. After-event LOS is sometimes a moving target due to blow- ing and drifting snow conditions. In this case, those condi- tions may be considered to be part of the event. In general, higher within-event LOS can be produced with an anti-icing strategy and relatively short operational cycle times of less than 1.5 hours. As cycle times increase, there are opportunities for higher accumulations of snow and ice on the roadway prior to plowing and retreating. Thus, main- taining an unbonded pavement/snow/ice interface becomes increasingly more difficult as cycle times increase. For the purpose of the following discussion, pavement con- dition LOS is divided into three categories of low, medium, and high that can be related to PSIC defined in Table 1 in the following way: Pavement condition LOS PSIC Low 5 and 6 Medium 3 and 4 High 1 and 2 With respect to after-event LOS, most agencies provide treatment until âbareâ pavement is achieved. The measure of LOS then becomes the time, in hours, needed to reach a high LOS (a PSIC of 2 or 1). Again, for the purpose of this dis- cussion, after-end-of-event LOS is divided into the three cat- egories of low, medium, and high in the following way: Time (hr) to achieve After-event LOS a PSIC of 2 or 1 Low >8.0 Medium 3.1â8.0 High <3.1 STRATEGIES AND LEVEL OF SERVICE Table 7 shows the expected LOS levels that can be achieved within- and after-winter weather events from various snow and ice control strategies and from tactics. For convenience, each strategy/tactic is described again below. It must be rec- ognized that these are general approaches and changing con- ditions within an event often necessitate changes in strategies and tactics. Anti-icing Anti-icing is a general strategy that attempts to prevent the formation of ice/pavement bond by the timely application of ice control chemicals. Chemicals may be applied before the event (pretreating), early in the event, and as necessary throughout the event. This strategy generally produces high LOS during and after the event. Deicing Deicing is a strategy of allowing ice/pavement bond to form during an event and periodically treating it with chemicals until the ice/pavement bond is broken and snow/ice can be mechan- ically removed or displaced by traffic. This strategy generally produced low to medium within- and after-event LOS. Mechanical Mechanical removal is the displacement of snow/ice from the roadway by plows, rotary plows (snow blowers), brooms, and other mechanical means. This approach, as a strategy, is capable of producing low within- and after-event LOS. At pavement temperatures above 32°F and below about 12°F, higher LOS may be possible with mechanical removal. Mechanical and Abrasives The practice of plowing snow and spreading abrasives (either straight or mixed with a small amount of chemical) is common on lower-volume roads. It also may be a necessary treatment due to low pavement temperatures. As a strategy by itself, it only is capable of producing low within- and after-event LOS unless a very warm pavement temperature above 32°F is involved that does not allow ice/pavement bond to occur.
Mechanical and Anti-icing Timely mechanical removal of snow/ice within an event, in conjunction with an overall anti-icing strategy, will pro- duce the highest possible LOS within and after events. Mechanical and Deicing Mechanical removal in conjunction with a deicing strategy within an event will produce low to medium LOS within and after winter weather events. This primarily results from con- trolling the depth of loose snow and ice on the roadway. Mechanical and Prewetted Abrasives Mechanical removal plus treatment with abrasives that have been prewetted with liquid chemical is capable of pro- ducing low within- and after-event LOS. Pavement temper- atures above 32°F that will not allow ice/pavement bond may allow higher LOS to be achieved. Limited research shows prewetting abrasives might produce a slightly higher LOS than a stockpile mix alone. Anti-icing for Frost/Black Ice/Icing Protection Use of a liquid ice control chemical for pretreating areas susceptible to frost/black ice/icing that may occur in the absence of precipitation is a proven effective anti-icing tac- tic that prevents ice formation. Since the ice does not form, the LOS is always high. 16 Mechanical and Abrasives Containing More than 100 lb/LM of Chemical âRichâ abrasives/chemical mixtures containing more than 20 percent chemicals by weight have been used for many years. They are capable of providing all ranges of LOS, depending on pavement and weather conditions. The LOS provided is generally in proportion to the amount of chemi- cal in the mix and the application rate. Research has shown that to produce a high LOS, a strategy of using chemicals alone will be more effective and less costly than using mix- tures of chemicals and abrasives. Chemical Treatment Before or Early in an Event, Mechanical Snow/Ice Removal During an Event, and Deicing at the End of an Event This is a hybrid strategy suitable for lower priority roads that produces a medium after-event LOS for a small chemi- cal investment. The initial chemical application seems to pre- vent a strong ice/pavement bond. This, in conjunction with the later chemical application and any solar pavement warm- ing, leads to a fairly quick recovery. This is particularly effec- tive when the chemicals are placed in a narrow band around the center of a two-lane crowned roadway. TREATMENT SELECTION When selecting treatments, the most important considera- tion is LOS goals. Depending on a variety of factors, the goals may change during an event. Every snow and ice control treatment should be individ- ually designed to produce an effect that is consistent with the LOS goals, weather conditions, pavement conditions, TABLE 7 Strategies and tactics and LOS expectations Within-event LOS After-event LOS Strategies and Tactics Low Medium High Low Medium High Anti-icing X X Deicing X X X X Mechanical X X Mechanical and Abrasives X X Mechanical and Anti-icing X X Mechanical and Deicing X X X X Mechanical and Prewetted Abrasives X X Anti-icing for Frost/Black Ice/ Icing Protection X X Mechanical and Abrasives Containing > 100 lb/LM of Chemical X X X X X X Chemical Treatment Before or Early in Event, Mechanical Removal During Event, and Deicing at End of Event X X
and available resources of the moment. Weather and pave- ment conditions are continually changing and may require tactical adjustments. LOS goals may be changing with the time of day and pavement conditions. Available resources may be changing with equipment breakdowns and manda- tory personnel rest periods. The actual formula or process for making wise and appro- priate treatment decisions is simple. It involves using timely 17 information on weather and pavement conditions plus having an understanding of the LOS goals and capabilities of avail- able resources. These resources include snow and ice control strategies and tactics, materials, equipment, and manpower. Attachment 1 provides recommended guidelines for using road and weather information to make snow and ice control treatment decisions. Chapter 8 provides recommended oper- ational guidelines for winter maintenance field personnel.
