when the rhine-ruhr stadtbahn network was planned in the early 1970s, standardised rolling stock was planned as well. at the same time, a second stadtbahn network was planned for cologne and bonn. because the future cologne stadtbahn already had one finished tunnel, that was built with the city's own money with streetcars in mind, the "stadtbahnwagen" designed for the rhine-ruhr network was not suitable. so, another vehicle was designed for the cologne/bonn network, that was capable of driving though tighter curves. this vehicle, now referred to as "stadtbahnwagen typ b" was immediately ordered by transport authorities in cologne and bonn, while rhine-ruhr authorities remained hesitant about "their" vehicle, now renamed "stadtbahnwagen typ a". eventually it was decided that the type "a" lrv was too unwieldy and type "b" lrvs were ordered by essen, mülheim, düsseldorf, duisburg and dortmund. the type "a" concept, which consists of close coupled two-car sets, was shelved and later revived for the stuttgart stadtbahn.