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    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
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      <title>Optimization of Spreads With an Increased Brine Content</title>
      <link>https://trid.trb.org/View/1522708</link>
      <description><![CDATA[The determination of optimized de-icing agent application rates for typical winter scenarios and each corresponding winter maintenance strategy have been in the focus of research at the Institute of Transportation Sciences of the Technical University of Vienna in the past years. Based on extensive field and lab research it was possible to determine the necessary application rate and timing based on precipitation, road surface temperature and traffic on the basis of a comprehensive holistic model. The model developed also allows estimating the development of skid resistance during maintenance intervals. This research was based on a spreading technique of pre-wetted salt called FS30. FS30 stands for a weight based mixture of 70% dry salt and 30% brine (with a 20% concentration). The brine is normally produced with sodium chloride. Based on a large number of measurements at different conditions, the amount of residual salt on the road surface over time was determined. Furthermore, these residual salt measurements allowed further insight into the impact of different traffic volumes and amounts of precipitation. Based on the results of freezing and thawing experiments the strategy of preventive salting was introduced into practices, above all to prevent freezing and slippery roads. With the success of this preventive treatment strategy the question was raised how spreading losses of salt could be reduced so as to lead to even better results. Examining the effect of pre-wetted salting based on different proportions of dry salt and brine up to an amount of 100% brine proved to be the best way. Based on further extensive testing it was possible to provide statistical evidence for an increased proportion of residual salt with higher portions of brine. Furthermore, a means for adapting existing equipment for higher fractions of brine and the optimal brine content for different situations were investigated. With this cost efficient approach already being introduced into practice it is possible to save about 20% of salt without the need of extensive reinvestments. Subsequently, this also leads to less environmental impacts while keeping the roads safe. Climate data over the period from 1896 onwards were evaluated by the Department of Hydrology of the Office of the Government of Lower Austria.. The mean change in air temperature of the past 100 years has resulted in an increase of the mean value of +0.7°C. This long-term evaluation also shows that in Austria snowy winters have increased in the past decade. In line with the climatic changes and the development of a new salt-saving and environmentally friendly salt spreading technique, analyses carried out show a decreasing tendency in the average salt consumption. In the past nine years, an average reduction in salt consumption per square meter salt-spreading-area of 39 g/m² to now 27 g/m² is demonstrated for a salt-spreading-day. This is a more than a 30% lower salt consumption while maintaining the high quality of winter maintenance.]]></description>
      <pubDate>Thu, 26 Jul 2018 14:42:50 GMT</pubDate>
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      <title>A Winter Maintenance Strategy for Roads Based on Climatic Factors</title>
      <link>https://trid.trb.org/View/899043</link>
      <description><![CDATA[The purpose of the report is to discuss the efficiency effect of different methods for friction control of roads on the safety and accessibility due to the climatic conditions, and to establish climatic parameters that may be helpful in selecting the strategies for winter maintenance. The report is based on the analysis of the data assembled for the VTI project “Winter Model”, and presents mainly comparisons between accident data, operational standards for winter maintenance and climatic conditions in the different regions of Sweden. In addition, recommendations for selecting strategies for winter maintenance are presented. Salt and gritting are the main methods for friction control on winter roads. In the latest years the method of using warm wetted sand has been developed and the method represents an alternative to salting in stable cold climates. The favorable weather situation for the warm wetted sand method is assumed to be road surface temperatures below -1°C and less than 3 mm water equivalent (WE) within 6 hours. The corresponding values for recommending salt are assumed to be above -8°C and less than 1 mm WE/hr. The basis for the data used in the present analyses is all police recorded accidents, except wildlife accidents, on the state roads in Sweden and data of road surface conditions recorded by the road authorities in the 1993/1994 to 1996/1997 winters. The accident data are broken down into: (1) Types of accidents and severity of the accidents. (2) Road conditions recorded by the police at the time of the accidents. (3) Vehicle mileage on the different road conditions. (4) Maintenance standard for the roads.  The accident analyses include only fatalities and severe injuries and are made separately for: (1) Four climatic regions; Southern, Central, Lower Northern and Upper Northern Sweden. (2) Three maintenance standard classes; A1+A2 and A3+A4, which require salting and B1+B2, which is based on gritting. (3) Two road conditions: bare roads and snow/ice covered roads. The accident rates for driving on snow/ice covered roads are dependent on the proportion of vehicle mileage on snow and ice relative to bare roads and the rates increase for lower proportions. The accident rate for snow/ice covered roads compared to bare roads is as high as 8–10 for vehicle mileage proportions of approximately 0.05 and 2–3 for proportions exceeding 0.5. For instance, 30–40 per cent of the accidents recorded on the A1+A2 roads in Southern and Central Sweden occurred during the 4 per cent of the time the roads were covered by snow or ice. The calculated numbers of accidents related to driving on snow and ice are lowest for the salted roads in the three southern regions of Sweden, but the opposite for Upper Northern Sweden, where there is a significantly higher number of accidents on the salted road network. The data material indicates that there is a maximum of accidents when the vehicle mileage ratios on snow and ice are between 0.3 and 0.4. If these indications are correct one should preferably introduce salting if the ratio of snow and ice on unsalted roads is 0.3–0.5 and the use of salt may reduce the ratio to less than 0.2. On the other hand, by introducing salt in climatic areas having ratios exceeding 0.5 and ending up with ratios close to 0.3 will probably increase the number of accidents. The ratio of the summer/winter accident rates for fatalities and severe injuries is higher for salted than for unsalted roads in all four climatic regions. The ratio is 1.2 for salted roads in the three southern regions and 1.4 for Upper Northern Sweden. The corresponding ratios for unsalted roads are 0.95 and 1.05. The data material makes it further possible to calculate the accident rates for driving on bare roads in the winter and compare these rates with the corresponding summer accident rates. The calculations indicate that the accident rates for driving on bare roads in winter are on average 0.55 for the unsalted roads and 0.75 for salted roads. Probably drivers expect on unsalted roads the roads to be partly covered with snow or ice in the winter and they reduce their speed even when the roads are bare. Similarly, drivers on salted roads expect the roads to be free of snow and have thus a higher speed when the roads are bare. The development of the warm wetted sand method and the experience with high accident rates in very cold climates should be reflected in the selection of strategies for the winter maintenance of roads. The report has introduced three climatic parameters, which are mainly recommended to be used on a monthly basis: (1) Winter Severity Index, Wsev; proportion of recordings < -8°C (2) Winter Stability Index, Wstab; proportion of days favorable for the warm wetted sand method (3) Winter Instability Index, Winst; proportion of fluctuations around 0°C per day. The high accident rates found for the salted road network in Upper Northern Sweden form the background for recommending that salt should not be used in areas with winter months having Wsev exceeding 0.2, which means that the 20 per cent of the recordings are below -8°C. In areas with such climate, the warm wetted sand method is usually a reliable alternative, even for relatively high traffic loads. The warm wetted sand method is most favorable in cold stable climates, but since the increase in cost compared to traditional gritting is relatively small, one may justify using warm wetted sand even in conditions when the probability of the long lasting effect is low. Warm wetted sand is only recommended for use in periods, and on roads with AADT <2,000, when the Winter Stability and the Instability Indexes are within the area represented by the following points in the Wstab-Winst diagram: (1) Wstab =1 and Winst =0; (2) Wstab =0.2 and Winst =0; (3) Wstab =0.4 and Winst =1.2. In areas and periods with lower values of Winst represented by these limits, traditional gritting is the only alternative to salt at present.]]></description>
      <pubDate>Mon, 31 Aug 2009 09:24:37 GMT</pubDate>
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