The advantage is that there are no shared sections of the route and thus delays on one line would not induce delays on others. As a disadvantage, the frequent need to change trains would make few one-seat-rides possible and make a trip e.g. from Erlenstegen to Zerzabelshof need several changes. The lines would have been as follows in this model:   In the end, the model R turned out to be the most useful of the four models in terms of urban planning, operational engineering and development possibilities. It was slightly modified and formed the basis of the "Nuremberg General Transit Plan" (GNVP) adopted on September 8, 1971 by the City Council. The planned subway network should thereafter consist of the three main lines, out of which the lines U2 and U3 should receive branching possibilities at the stations Friedrich-Ebert-Platz (direction Thon), Rathenauplatz (direction Erlenstegen), Steinbühl (direction Gartenstadt) and Schlachthof (direction Gebersdorf). One point of criticism is the insufficient consideration of the territories incorporated into the GNVP on July 1, 1972 (when several suburbs were annexed into Nuremberg in the course of a Bavaria-wide redrawing of municipal boundaries), since subway planning was only slightly adapted to the new settlements. On 20 March 1967, German transport minister Georg Leber and Nuremberg "Oberbürgermeister" ("Lord Mayor") Andreas Urschlechter (both SPD) had the honour of "striking the first blow" for the new metro. This was done in Bauernfeindstraße when they triggered the pile driver. On 1 March 1972, the first stretch of the system opened, U1 Langwasser Süd to Bauernfeindstraße. Over the next few years, further stretches of U1 were opened. Uniquely, the metro was built "from the outside in", starting in the rather outlying area of Langwasser before reaching the historical core and the central train station. On 28 January 1984, Nuremberg's second U-Bahn line, U2, went into service between Plärrer and Schweinau. This line, too, underwent further extensions, eventually even reaching the airport in 1999. Expansions of the subway were often accompanied with the closure of nearby tram lines, which was initially not opposed by most of the city's population.