Snow and Ice Control: Guidelines for Materials and Methods (2004)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

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

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