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1 CHAPTER 1 INTRODUCTION Snow and ice control on the U.S. highway system consumes Mechanical removal of snow and ice together with fric- over $2 billion in direct costs each year (1). Indirect costs asso- tion enhancement, and ciated with corrosion and environmental impacts add at least Mechanical removal alone. $5 billion (1). Strategies and tactics that employ solid and liquid chemicals, abrasives, and mechanical methods-- Roadway anti-icing is a snow and ice control strategy of individually or in combination--have been used by different preventing the formation or development of bonded snow and state and local agencies. Research by the Strategic Highway ice to a pavement surface by timely applications of a chemi- Research Program (SHRP), the Federal Highway Adminis- cal freezing-point depressant. The tactics employed during tration (FHWA), the American Association of State High- anti-icing operations consist of chemical applications that are way Officials (AASHTO), the National Cooperative Highway coordinated with plowing. Research Program (NCHRP), and other organizations in the Deicing is a snow and ice control strategy of destroying United States and other countries has addressed many of the the bond between snow and ice and the pavement surface by issues associated with snow and ice control treatments (25). chemical or mechanical means or a combination of the two. However, widely accepted guidelines for selecting level-of- Mechanical removal of snow and ice together with friction service (LOS)-driven roadway snow and ice control strate- enhancement is a strategy in which abrasives or a mixture of gies and tactics for specific climatic, site, and traffic condi- abrasives and a chemical are applied to a layer of compacted tions have not been developed. Without this information, the snow or ice already bonded to the pavement surface that may process of selecting treatment strategies and tactics that meet or may not have been partially removed by mechanical means highway agencies LOS objectives is difficult. (plowing and scraping). This strategy is used to provide an This report presents a realistic set of guidelines for select- increase in the coefficient of friction for vehicular traffic, ing roadway snow and ice control strategies and tactics for a although this increase may be short lived. Abrasives, by them- wide range of climate, site, and traffic conditions found in the selves, are not ice control chemicals and will not support the United States. These guidelines apply to both state and local fundamental objective of either anti-icing or deicing. highway agencies. The term "roadway" used in this docu- Mechanical removal alone is a strategy that involves the ment refers to any highway, road, street, or other paved sur- physical process of attempting to remove an accumulation of face that carries motor vehicles. snow or ice by means such as plowing, brooming, blowing, The guidelines were developed from appropriate existing and so on, without the use of snow and ice control chemicals. documentation plus data collected from field testing of selected This strategy is strictly a physical process that has some merit snow and ice control strategies and tactics over three winters. during and/or after frozen precipitation has occurred at very In the general sense, a strategy is a careful plan or method low pavement temperatures, say below 15F, and on very directed at achieving a specific goal or goals. Tactics, on the low volume and unpaved roads. other hand, are the systematic employment of available means The guidelines were developed to assist maintenance man- agers, local maintenance supervisors, and other field person- or resources to accomplish a desired end condition of a strat- nel in selecting LOS-driven roadway snow and ice control egy. For purposes of these guidelines, strategies and tactics strategies and tactics. The guidelines focus on the snow and refer to the combination of material, equipment, and methods, ice control materials and methods that best address such items including both chemical and physical, that are used in snow as LOS, weather, site, and traffic conditions. and ice control operations to achieve a defined level of service. Following this Introduction, the guidelines are divided into The various roadway snow and ice control strategies used seven major chapters: in winter maintenance operations in the United States can be classified into four general categories: Chapter 2: Level of Service--This chapter describes the various winter-time LOS definitions used by highway Anti-icing, agencies in the United States. Stressed is the need to Deicing, define LOS in terms of measures of effectiveness that can

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2 be used by the agencies in their evaluation process. Fac- Chapter 5: Strategies and Tactics and Their Appli- tors affecting LOS are discussed in general and then more cation to Support Level of Service Choices--This specifically in later chapters. The discussion includes the chapter describes the four snow and ice control strate- need for describing within-storm, end-of-storm, and post- gies: anti-icing, deicing, mechanical removal of snow or storm conditions when developing LOS. ice with traction enhancement, and mechanical removal Chapter 3: Snow and Ice Control Operational Con- of snow or ice. For each of these strategies, the guide- siderations--This chapter describes the various climatic, lines describe the effects of climate, site, and traffic site, and traffic conditions found in the United States that considerations. In addition, and considering PSIC and are considered important in the selection of appropri- LOS, the guidelines discuss the strategies with respect ate roadway snow and ice control strategies and tactics. to pre-storm, within-storm, and end-of-storm operations. Described are the various types and distribution of win- Various tactics that can be used to support each of the ter weather conditions within the general climates of the strategies are also discussed. The chapter concludes United States. and their relationship to snow and ice con- with special discussions of traction enhancement and trol. This chapter also contains a description of micro- the use of combinations of strategies and tactics. climates and their importance in selecting appropriate Chapter 6: Factors Influencing the Choice of Materi- strategies and tactics for snow and ice control. Those als, Their Form, and Associated Application Rates-- site conditions that influence snow and ice control are In order to attain LOS classes, managers must select discussed. Major influences include the area develop- appropriate resources. This chapter first describes the influence of pavement temperatures and the dilution ment setting, roadway features, and solar influences. potential of winter weather events. Then discussed are Also described are the influences of site considerations the properties of materials used in support of strategies on LOS goals that are achievable with various resources. and tactics and the effects of dilution with respect to This chapter also describes the traffic-related influences attaining LOS goals. on snow and ice control. The influences include traffic Chapter 7: Recommended Snow and Ice Control volume, vehicle mixes, essential or functional traffic pat- Practices--This chapter describes a recommended terns, and vehicle speeds. The influence of traffic con- process and sets of procedures to follow for snow and siderations on LOS is presented. Finally, this chapter ice control operations for various LOS goals. The rec- concludes with a summary of the important factors of ommended practices are based on the results of the these three considerations that influence the choice of strategies and tactics evaluated in this project, supple- snow and ice control strategies and tactics. mented by data assembled from various sources. A dis- Chapter 4: Performance-Based Level of Service-- cussion on treatment decision making concludes the This chapter describes a process for use by agencies in chapter. developing a performance-based LOS. This discussion Chapter 8: Recommended Operational Guidelines includes the use of Pavement Snow and Ice Condition for Winter Maintenance Field Personnel--This chap- (PSIC) indices, a suggested set of PSIC definitions, and ter contains tables that suggest appropriate maintenance the establishment of LOS classes using PSIC for vari- actions to take during various strategy and tactic opera- ous highway classifications and for within-storm and tions for winter weather events. These tables are suitable end-of-storm conditions. for reproduction and use by field personnel.