Safe cycling in winter: Results of a case study on the role of de-icing in the city of Hamburg, Germany.

In parts of Europe and North America, cycling volumes decrease in winter due to a reduction in subjective safety. To counter this, high-quality winter maintenance is required on cycle paths. At the moment, grit and sodium chloride are considered state-of-the-art gritting/de-icing materials in Germany. However, grit has to be removed after winter because it poses a serious injury risk on dry streets, and, in various German cities, using sodium chloride is prohibited on segregated bike paths due to the harmful impact on surrounding trees. Therefore, there is a need for alternative gritting/de-icing materials. We used a mixed-methods approach consisting of qualitative and quantitative surveys together with laboratory investigations and a life cycle assessment to find suitable alternatives to sodium chloride and grit for use on segregated bike paths, and tested four de-icing materials (sodium chloride as a reference, sodium formate, calcium magnesium acetate or CMA, and potassium acetate) at two sites in Hamburg, Germany. The tests were accompanied by on-site cyclist surveys. The results show that the use of alternative (non-sodium chloride) de-icing materials either reduces or eliminates negative impacts on the environment at a local level, for example on trees along the cycle path. However, this reduction goes hand in hand with increasing negative environmental impacts at a global level due to higher overall emissions associated with the tested alternative de-icing materials. Regarding cyclists' safety, sodium formate was the only de-icing material which delivered comparable results to sodium chloride and should therefore be tested in extended conditions. Further research is needed on the large-scale application of the investigated de-icing agents on cycle paths in different cities, along with a survey of a larger number of cyclists. A final evaluation of the environmental aspects can only be made when the supply and production conditions for large-scale use are clear. Basically there are two options for the practical application of de-icing materials: The usage of the costlier alternatives with better properties at a local level in the hope of fast development towards a better global GHG footprint in their manufacturing processes, or sticking to the use of grit and sodium chloride (where it is possible) while committing to improving clean-up after the snow and ice melt to prevent unsafe road conditions in spring.

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.