Holz-Rau, Christian, and Joachim Scheiner. “Road Traffic Safety in North Rhine-Westphalia Districts: Where Do We Live Most Safely?”. Raumforschung Und Raumordnung | Spatial Research and Planning, vol. 68, no. 5, Oct. 2010, pp. 357–371, https://doi.org/10.1007/s13147-010-0047-1.