In 1996, the DIN, the German Institute for Standardization, issued the DIN 18024 part 1 ("Barrierefreies Bauen – Teil 1: Straßen, Plätze, Wege, öffentliche Verkehrs- und Grünanlagen sowie Spielplätze; Planungsgrundlagen" / Barrier-Free Design – Part 1: Streets, Places, Roads and Recreational Areas; Planning Basics), updated in 1998. Kassel had been at the forefront, performing tests with low-floor buses as early as 1992. A simple increment on the bus platform height showed problems with wear on the bus tyres, and the planning department of the Kassel public transport company began to assemble ideas on a "special curb" ("") for their bus stops in 1994. A manufacturer was found in in Gensungen south of Kassel with their patent kerb (EP0544202/1993). After its termination manufacturing was taken over by in Borken, Hesse (also south of Kassel). By 2001 about 16% of bus stops in Kassel had been converted to "Kasseler Sonderbord".