Huber et al. (2016) Huber M., Welker A. & Helmreich B. (2016). Critical review of heavy metal pollution of traffic area runoff: Occurrence, influencing factors, and partitioning. Science of the Total Environment, 541, 895-919. https://doi.org/10.1016/j.scitotenv.2015.09.033. Median values, 21 roads with low traffic intensity 100-4000 vehicles/day.