In response to changing regulations and increasing environmental concerns related to salt application on roads, the Norwegian Public Road Administration (NPRA) initiated a four year research and development project, entitled: ”Salt SMART”.
The motivation for the project is the increasing focus on the negative environmental effects related to the use of salt (sodium chloride) on roads in wintertime. Excessive salt concentrations have been measured in different Norwegian groundwater sources and the insufficient oxygen levels measured in the bottom water layer of different Norwegian lakes has been shown to be directly related to elevated salt concentrations. Meanwhile, the amount of salt applied annually on Norwegian roads increased significantly in the past few years. Added to these concerns, a new EU Water Framework Directive is currently being implemented in Norwegian water management regulations. These regulations place pressure on the NPRA to control its discharges of salt (sodium chloride) into ground and surface water.
Salt application is an important measure to maintain road accessibility and traffic safety during wintertime. It prevents and removes ice deposition, hampers the compaction of snow and reduces the adhesion of snow on the road surface.
The project’s primary objective is to promote a justifiable (responsible) use of salt for winter maintenance purposes. The project has adopted the principle that road accessibility and traffic safety is to be ensured without unacceptable impact on the environment. This principle serves as a reference throughout the project.
The following tasks of the project were defined:
- to provide a knowledge base for a justifiable use of salt in winter maintenance by collecting, systemising, and developing general knowledge and practices;
- to identify vulnerable areas within Norway;
- to investigate and develop alternative winter maintenance practices that ensure road accessibility and traffic safety in vulnerable areas;
- to develop maintenance strategies to promote justifiable salt use for less vulnerable areas.
The project has following results:
• Doctoral studies, post-doctoral research positions and master’s theses that have provided more basic knowledge about how chemicals work in winter operations.
• Field tests to study whether additives in salt increase the time that salt remains on the road surface – with a view to being able to salt less frequently. No special effect from the tested substance was shown.
• Experimentation with various forms of spreading: salt solution, salt slurry, moistened salt and dry salt. Salt solutions have proved to have the most long-lasting effect on dry or slightly wet road surfaces. During winter 2010/2011 experiments using salt slurry - a type of “porridge” made of fine-grain salt - will be conducted.
• Experimentation with intensified and alternative forms of snow removal. The less snow remaining on the road, the less salt we need to use. On E39 at Ålesund, experiments were conducted during winter 2009/2010 using special equipment designed to sweep the snow off the road surface (the same type of equipment used at airports). Calculations show that by using this kind of equipment while at the same time using a salt solution rather than moistened salt, the total amount of salt used can be reduced by approximately 40 percent.
• Review of the literature on alternatives to salt (natrium chloride) and additives designed to improve the effect of salt. No chemical emerges as a good alternative to salt. Certain substances have the same or a somewhat better effect on road surfaces, but they also have the same or even worse negative effects on materials and the environment. Otherwise, the survey shows that scientific experiments have been conducted using additives to salt, but that knowledge is lacking in the field.
• Survey of the literature pertaining to environmental consequences from the use of various chemicals. This summarizes what has been learned, as well as knowledge that is lacking in the area – both nationally and internationally
Seeking for alternatives of salt for using on roads in winter.
Reducing of negative impact on salt used for roads i winter on the environment.