Utvärdering av sopsaltning på cykelstråk i Stockholm vintern 2016/17

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In Stockholm, cycling as a mode of transport is promoted, especially for commuting. Public transport as well as the roadway network has reached capacity during peak hours and cycling is considered to be an advantageous alternative, since there are environmental and health benefits to gain. To encourage people to cycle during winter and at the same time reduce the number of single bicycle crashes, a high winter maintenance service level is needed. Using salt for skid control of bicycle paths could be one solution, although it has its drawbacks and difficulties. In recent years, a method using a frontmounted power broom for snow clearance and salt for de-icing (commonly called “sweep-salting”) has become popular for winter maintenance of bicycle paths in Sweden.

In 2013 the city of Stockholm decided to try the “sweep-salting” method and evaluate its potential to improve the service level on bicycle routes for commuting. To optimize and develop the method, VTI has performed field studies every winter since 2013. These studies have included measurements of friction, road condition observations, measurements of residual salt on bicycle path surfaces, salt deposition at the side of bicycle paths, maintenance protocols and interviews with maintenance operators. Since all studies were done in field, in a real-life environment, the experimental work was designed according to the winter maintenance routines of the municipality and other prevailing conditions and circumstances. This report presents the results from the evaluation of the winter of 2016/2017.

The evaluations show that when working successfully, the sweep-salting method creates a bare surface with higher friction than traditional ploughing and gritting. Measures must be done in time and the operating speed adjusted according to the prevailing conditions. In mild weather brine is sufficient, but with lower temperatures and heavy snowfall larger amounts of salt is needed and pre-wetted or dry salt must be used. For the method to work properly, the bicycle path construction should be of good condition without cracks or other damages in the surface. Otherwise, it is difficult to clear the surface with the broom as snow and water can be trapped in potholes and cracks, eventually creating ice patches. A sufficient drainage from the surface is also crucial as every contribution of water will dilute the salt amount on the path with a following risk of creating a slippery surface. Narrow passages and obstructing design features cause difficulties when clearing the snow, resulting in a need of larger amounts of salt to prevent icy conditions. Clearing the surface from snow and water is crucial to get a good result with the method.

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