Deicing chemicals, along with plowing and sanding, are important tools for highway snow and ice control. For many years, however, it has been widely acknowledged that the most popular deicing chemical, sodium chloride or common road salt, has many unintended and often costly side effects. The last major efforts to estimate the true cost of salt were conducted 10 to 20 years ago. Today, however, many of the findings from these studies are no longer accurate, because knowledge and understanding of salt’s adverse effects have increased and, in some cases, significant steps have been taken to help control them. Unfortunately, the lack of more up-to-date cost information has contributed to confusion over the benefits and savings that might be achieved by using less harmful but higher-priced alternatives to salt that have been developed in recent years, such as calcium magnesium acetate (CMA). Recognising this need, Congress called on the U.S. Department of Transportation (DOT) to sponsor a study examining the total cost of salt and CMA, including the direct cost of application and indirect costs to the environment, infrastructure, and motor vehicles. The National Academy of Sciences was identified as an organisation to conduct the study.’ The National Research Council, which is the principal operating arm of the Academy, appointed a special study committee under the auspices of the Transportation Research Board (TRB) and the leadership of John J. Henry, Director of the Pennsylvania Transportation Institute at The Pennsylvania State University. Committee members are experts in chemistry, materials science, economics, environmental science, and highway engineering, operations, and maintenance. Congress requested that the study examine the full economic costs of using salt and CMA for highway deicing. In sponsoring the study, the Federal Highway Administration (FHWA) of DOT asked TRB to examine each deicer for both general deicing and selective uses, such as in environmentally sensitive areas and on corrosion-prone bridges. In approving the project, the TRB Executive Committee requested that the study committee also consider and comment on other promising deicing alternatives to salt and CMA when appropriate. Much of the report focuses on defining the true cost of salt, which is the most popular deicer and the standard of comparison for most other deicing products. After reviewing the evidence, the committee estimated many of salt’s costs in monetary terms, but often had to rely on a combination of sparse quantitative data, simplified assumptions, and its own expert judgement to do so. In some cases, however, a lack of sufficient information prevented even rough approximations of cost. Although the committee debated whether to assign monetary values to environmental damages, it did not for the following reasons: (a) the environmental effects of salt vary widely by location; (b) not enough information is available to determine the extent of environmental damage, even in nonmonetary terms (e.g., number of trees harmed); and (c) the valuation of environmental damage is highly subjective. Nevertheless, the committee did present several hypothetical environmental cases in Chapter 4 that contain estimates of the monetary costs involved in correcting or mitigating environmental damage from road salt. Although these cases are not representative of all highways on which salt is applied, they illustrate the potential scale of environmental costs attributable to salt use, and they are indicative of the kinds of data and analyses that are needed to estimate the nationwide environmental costs of road salt in monetary terms. In considering CMA, the committee summarised what is known about its field performance, compatibility with highway and automotive materials; environmental impacts, and production technologies and price. This task was complicated by the relatively small quantities of CMA used to date. Although the congressional request for the study focused on salt and CMA, at the outset of the study the committee hoped to include other deicing treatments (e.g., salt substitutes and additives) in its investigation. Whereas some references to other treatments are included in the report, the committee found too few independent analyses of them (many of which are proprietary commercial products) to draw conclusions. Salt, on the other hand, has been heavily researched, and CMA has been subjected to numerous government-sponsored evaluations. As a result, the committee focused on these two products. The committee stopped short of recommending that CMA be used in specific situations, because such conclusions can be reached only after in-depth consideration of local circumstances and ah other deicing treatments and mitigation measures available. Instead, the main purpose of the report is to provide general background information and reference material for highway agencies that may be unfamiliar with CMA, as well as those trying to get a better handle on the overall cost of their salting programs. The final report of the committee was reviewed by an independent group of reviewers in accordance with National Research Council report review procedures. (Author/publisher)
Samenvatting