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15 CHAPTER 7 RECOMMENDED SNOW AND ICE CONTROL PRACTICES The goal of effective snow and ice control programs each strategy/tactic is described again below. It must be rec- should be to provide the highest LOS possible within the ognized that these are general approaches and changing con- constraints of available resources and environmental responsi- ditions within an event often necessitate changes in strategies bility. LOS goals are viewed from the time frames of within- and tactics. 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- Anti-icing tions may be considered to be part of the event. In general, higher within-event LOS can be produced with Anti-icing is a general strategy that attempts to prevent the an anti-icing strategy and relatively short operational cycle formation of ice/pavement bond by the timely application of ice times of less than 1.5 hours. As cycle times increase, there control chemicals. Chemicals may be applied before the event are opportunities for higher accumulations of snow and ice (pretreating), early in the event, and as necessary throughout on the roadway prior to plowing and retreating. Thus, main- the event. This strategy generally produces high LOS during taining an unbonded pavement/snow/ice interface becomes and after the event. 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, Deicing and high that can be related to PSIC defined in Table 1 in the following way: Deicing is a strategy of allowing ice/pavement bond to form during an event and periodically treating it with chemicals until Pavement condition LOS PSIC the ice/pavement bond is broken and snow/ice can be mechan- ically removed or displaced by traffic. This strategy generally Low 5 and 6 produced low to medium within- and after-event LOS. Medium 3 and 4 High 1 and 2 Mechanical With respect to after-event LOS, most agencies provide treatment until "bare" pavement is achieved. The measure of Mechanical removal is the displacement of snow/ice from LOS then becomes the time, in hours, needed to reach a high the roadway by plows, rotary plows (snow blowers), brooms, LOS (a PSIC of 2 or 1). Again, for the purpose of this dis- and other mechanical means. This approach, as a strategy, is cussion, after-end-of-event LOS is divided into the three cat- capable of producing low within- and after-event LOS. At egories of low, medium, and high in the following way: pavement temperatures above 32F and below about 12F, higher LOS may be possible with mechanical removal. Time (hr) to achieve After-event LOS a PSIC of 2 or 1 Low >8.0 Mechanical and Abrasives Medium 3.18.0 The practice of plowing snow and spreading abrasives High <3.1 (either straight or mixed with a small amount of chemical) is common on lower-volume roads. It also may be a necessary STRATEGIES AND LEVEL OF SERVICE treatment due to low pavement temperatures. As a strategy by itself, it only is capable of producing low within- and Table 7 shows the expected LOS levels that can be achieved after-event LOS unless a very warm pavement temperature within- and after-winter weather events from various snow above 32F is involved that does not allow ice/pavement bond and ice control strategies and from tactics. For convenience, to occur.