consistently operated with old, repaired and partially rebuilt trams, as new ones could be purchased only from 1951 onwards. Even in the 1950s, new trams were consistently obtained in series of only limited numbers, as from 1955 the abolition of the tramway in Vienna was the contemporary transport planning vision, and investments were made accordingly. In their early to mid-20th century, private cars had been the exception in European cities, because they had then been too expensive for most of the population. However, with the growth of private transport in the postwar period, the calls for a car-friendly city became louder. Rail traffic on the road was therefore seen as a "transport barrier" (the term "transport" applying only to motor vehicles), and the full relocation of public transport to the U-Bahn and buses was seen as the vision of the future. In 1956, Vienna's first articulated trams, designated as Type D, were commissioned from Gräf & Stift. Due to the tight financial situation, the new trams were assembled from salvaged parts. The basis of each one was two old Stadtbahn trailer chassis, on which modern car bodies were mounted. The chassis and bodies were then connected, by means of a telescopic joint section, of Italian design. The prototype of the Type D, with road number 4301, was delivered on 3 July 1957. After the testing and commissioning process had been completed, the Type D entered service from 17 February 1958. The inaugural trip operated by these trams was on Line 71. A total of 16 type D trams were built. They were used until 1976 on Lines 9, 41, 42 and E2. They were cumbersome, due to their high weight (), and were also otherwise unconvincing. Changes, new trams, pre-metro and U-Bahn construction In 1958, at the time of conversion of the short Line 158, the practicality of using buses to replace trams was tested. From 1960, there was ongoing conversion of sections of track running through narrow streets in the densely built up areas within the Gürtel; the best known example is line 13 from Wien Südbahnhof to Alserstrasse. However, individual sections on the periphery of the city, and in surrounding communities beyond the city limits, such as the former steam tramway lines to Mödling and Groß-Enzersdorf, were replaced by bus lines. In the 1960s, a pre-metro system was built to move tramway sections under surface, that - according