Click for next page ( 12

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 11
11 CHAPTER 5 STRATEGIES AND TACTICS AND THEIR APPLICATION TO SUPPORT LEVEL OF SERVICE CHOICES As stated in the Introduction, the various roadway snow DEICING and ice control strategies used in winter maintenance opera- tions can be classified into four general categories and are Deicing is a snow and ice control strategy of removing discussed in details in this chapter: compacted snow or ice already bonded to the pavement sur- face by chemical or mechanical means or a combination of Anti-icing, the two. Deicing, Deicing is a suitable strategy for most weather, site, and Mechanical removal of snow and ice together with fric- traffic conditions except when the pavement temperatures are below 20F. Deicing operations can be accomplished at tion enhancement, and Mechanical removal alone. temperature lower than 20F, but the number of chemical applications and/or chemical application rates will be exces- sive, as shown in Attachment 1, and the time to accomplish deicing will be long. Chemical treatments are usually initi- ANTI-ICING ated later in a winter weather event and continued well after the end until a satisfactory pavement condition is reached. Roadway anti-icing is a snow and ice control strategy of pre- Deicing usually produces lower within-winter weather event venting the formation or development of bonded snow and ice and after-winter weather event levels of service. Deicing usu- to a pavement surface by timely applications of a chemical ally will require more chemicals than anti-icing to produce freezing-point depressant. The tactics employed during anti- the same LOS. icing operations consist of chemical applications that are coor- dinated with plowing. Anti-icing is suitable for use during most weather, site, and MECHANICAL REMOVAL OF SNOW AND ICE traffic conditions. It is particularly beneficial as a pretreat- TOGETHER WITH FRICTION ENHANCEMENT ment using liquid chemicals for anticipated frost and prefer- ential icing situations. Anti-icing with a liquid chemical is a Mechanical removal of snow and ice together with friction good strategy when the pavement temperatures are above enhancement is a strategy in which abrasives or a mixture of about 20F at the onset of a snowfall event. It is not a good abrasives and a chemical are applied to the plowed or scraped strategy when the pavement temperatures are below about roadway surface that may have a layer of compacted snow or 20F at the onset of a snowfall event, or at any freezing pave- ice already bonded to the pavement surface. This strategy is ment temperatures when the snowfall event is preceded by used to provide an increased level of friction for vehicular rain. Anti-icing with liquid chemicals is not recommended traffic, although this increase may be short lived. Abrasives, during freezing rain or sleet events. Anti-icing with solid or by themselves, are not ice-control chemicals and will not sup- prewetted solid chemicals is not a good strategy when the port the fundamental objective of either anti-icing or deicing. pavement temperatures are below about 15F at the onset of This strategy has been used for many years in most snow a winter weather event. The use of chemicals below these min- and ice situations; however, its only real applications are in imum pavement temperatures will require excessive amounts very low pavement temperature situations (about 12F) where of chemicals to be used as shown in Attachment 1. chemical treatments are not likely to be effective and on Anti-icing can be initiated before a winter weather event or roads having a low traffic volume and a LOS designation. very early in the event. By continuing the strategy throughout This strategy is sometimes used when agencies run out of the event there should be a very rapid recovery or achievement chemical deicers. of a satisfactory pavement condition after the end of the The LOS expectation (within-event and after-end-of-event) event. Anti-icing produces very high within-winter weather for this strategy cannot be high unless there are significant event and after-winter weather event LOS. amounts of ice control chemicals in the mixture, unless there