Manual of Practice for An Effective Anti-Icing Program - A Guide for Highway Winter Maintenance Personnel

1. INTRODUCTION

Application of a chemical freezing-point depressant onto a highway pavement at the start of a winter storm, or even prior to the beginning of precipitation, inhibits the development of a bond between the snow or ice and the pavement surface. Furthermore, moderate and periodic reapplications of the chemical during the storm can continue this effect. Such preventive operations are the core of an anti-icing program.

Anti-icing is the snow and ice control practice of preventing the formation or development of bonded snow and ice by timely applications of a chemical freezing-point depressant. It provides a maintenance manager with two major capabilities: the capability for maintaining roads in the best conditions possible during a winter storm, and the capability to do so in an efficient manner. As a consequence, anti-icing has the potential to provide the benefit of increased traffic safety at the lowest cost. However, to achieve this benefit the maintenance manager must adopt a systematic approach to snow and ice control and must ensure that the performance of the operations is consistent with the objective of preventing the formation or development of bonded snow and ice. Such an approach requires use of considerable judgment in making decisions, requires that available information sources be utilized methodically, and requires that the operations be anticipatory or prompt in nature.

In contrast to anti-icing operations, a common procedure of traditional snow and ice control practice is to wait until an inch or more of snow accumulates on the pavement before beginning to plow and treat the highway with chemicals or abrasives. While this procedure is straight-forward, it frequently leads to a compacted snow layer (pack) that is tightly bonded to the pavement surface. A subsequent "deicing" of the pavement is then necessary, usually requiring a large quantity of chemical to work its way through the pack to reach the snow/pavement interface and destroy or weaken the bond. Because this operation is reactionary, it requires less judgment than anti-icing. Yet as a result of its inherent delay, it often provides less safety, at higher cost, than anti-icing. Nonetheless the reactive technique of deicing will remain important for snow and ice control, as there will always be lower priority service levels that preclude preventive operations.

Anti-icing is well suited to routes with a higher level of service. This is because the vigilance and timeliness of successful anti-icing operations are most compatible with service levels requiring earlier and higher frequency winter maintenance operations. It is also because the preventive nature of anti-icing can support higher service level objectives such as maintaining bare pavement throughout a storm or returning to bare pavement as soon as possible following pack formation. In fact, because of the demanding requirements of higher service levels, many maintenance forces in the United States have been instinctively implementing elements of anti-icing practices for years. Sufficient evidence has accumulated from 2 years of Strategic Highway Research Program (SHRP) and 2 years of Federal Highway Administration (FHWA) anti-icing testing to demonstrate the effectiveness of US anti-icing practices, which has culminated in this manual.

1.1 PURPOSE OF THE MANUAL

This manual provides information for successful implementation of an effective anti-icing program. It is intended for use by highway agency maintenance managers at headquarters and subareas as well as field personnel.

The manual is written to guide the maintenance manager in developing a systematic and efficient practice for maintaining roads in the best conditions possible during a winter storm. It describes the significant factors that should be understood and must be addressed in an anti-icing program, with the recognition that the development of the program must be based on the specific needs of the site or region within its reach. It focuses on the weather information, materials, and methods that will best address site conditions such as level of service, highway agency resources, climatological conditions, and traffic.

1.2 SCOPE AND ORGANIZATION OF THE MANUAL

Following the Introduction, this manual is divided in three sections plus appendixes:

• Section 2 presents an introduction to anti-icing in the context of an agency’s winter maintenance program.

• Section 3 describes the operational, decision making, and personnel management capabilities needed to support an anti-icing program. It contains three major components: operations toolbox, decision-making toolbox, and personnel toolbox.

• Section 4 describes the operations and practices of anti-icing. It includes recommendations for successful anti-icing practices that can be employed for various combinations of precipitation, temperature, traffic volumes, and mandated levels of service. It complements the information provided in section 3, and serves as a companion and background document for the specific and concise guidance in Appendix C. The Section contains four major components: initial operations, subsequent operations, special considerations, and post-storm assessment of operations. It and the guidance of Appendix C are based on analysis of data obtained during the winters of 1993/94 and 1994/95 in the 15 States participating in the FHWA Test and Evaluation Project 28 (T&E 28) ⁽¹⁾ [ Underlined numbers in parentheses refer to references at the end of this document.] , and also on the relevant experience and review of anti-icing practices from SHRP Project H-208 ⁽²⁾.

• Supporting and auxiliary material regarding chemicals is presented in the Appendixes A and B. Appendix C presents guidance for conducting anti-icing operations during specific precipitation and weather events.