HARMONIZATION OF LOAD RESTRICTIONS FOR FROST-THAW DAMAGE

Within the framework of Finnra's strategic research program S14: "Economical Maintenance of Low Volume Roads", Roadscanner Oy and Plaana Oy have been assigned to conduct a multifaceted survey. The main focus of this survey has been to collect information on the current load restriction policies in Finland as well as the rehabilitation methods used on roads with spring thaw weakening problems and their effectiveness. The assignment also included developing a proposal for a harmonized national load restriction policy. The report begins with a summary of the material, compiled during the project through literature reviews and interviews, concerning the current load restriction policies in the Nordic countries and North America. The second part of the report describes a new classification system for the implementation of load restrictions on gravel roads and roads paved with a surface dressing or soft bitumen asphalt. In this system, gravel roads are divided into three classes: In class 0, load restrictions are not required (0A) or not allowed (0B). For roads in class 1, the need for load restrictions is judged each year based on a spring-thaw weakening prognosis. For roads in class 2, load restrictions can be used every spring, if the situation requires it. The classification guidelines are partly based on the model used in Sweden, which is considered to be a well functioning classification system, as it uses, among others, the amount of spring thaw damage observed as a classification criteria. This classification system also takes into account the importance of the road to local industries: as load restrictions are categorically not allowed on the most critical road connections, the district road authority should in these cases take immediate measures to rehabilitate a weakened road. The report also proposes guidelines for determining the starting and ending of a load restriction period. The new load restriction classification system was tested in spring 2003 in the area around Kemijarvi. The report presents a summary of the results from the field trial. The effects of introducing the new classification system, with regard to current practice, were projected through comparison calculations done with the data provided by the Hame, Savo-Karjala, and Lappi road regions of Finnra. The test results along with commentaries from the regional road authorities are also published in this report.