1895, Edison had replaced the SAO in managing the network. Electrification was completed in 1901. In 1910, following an expansion of the network, line numbering was introduced, using numbers from 1 to 30. The early ATM years (1917–45) In 1917, the comune of Milan assumed direct control of the city's tramway network, through the Ufficio Tramviario Municipale. A new corporation, the Azienda Tranviaria Municipale (ATM), was established to manage the network's operations. In 1926, the network was substantially reformed. The so-called "carousel" terminus in Piazza del Duomo, which had become a source of traffic problems for Milan's emerging automobile traffic, was closed. The radial lines previously focused on that terminus were transformed into "V" shaped lines, which called instead at one of two terminals located relatively close together. Additionally, in an effort to discourage passengers from taking unnecessarily long journeys, ATM started selling tickets for single trips, with no set period of validity. From the following year, until 1930, the 502 members of the now famous series 1500 trams entered Milan's tramcar fleet. These trams, many of which are still in service, were modelled on the then most modern American Peter Witt streetcars. In 1931, a few tram lines were modified to serve the new Milano Centrale railway station, located several hundred metres north of its predecessor. The first trolleybus routes in Milan commenced operations in 1933. However, in contrast with many Italian cities, Milan did not replace its trams with this new form of public transport. Trolleybuses were used instead to complement the trams on peripheral routes, and in particular, on Milan's outer ring road. The tramway network, which had been further extended, was still efficient (thanks to Milan's wide streets and many private homes), and was all double track, with spacious and modern tramcars. In the same year, many of the city's bus routes were extended, particularly to outside locations that had been annexed to the comune of Milan in 1923. In 1939, the extensive long-distance tramway network, electrified in the previous decade by the Società Trazione Elettrica Lombarda (English: Electric Traction Company of Lombardy) (STEL), came under the management of ATM. The urban tramway network reached its peak in the same year. World War II caused serious damage to that network, but the damage was soon repaired. Contraction and revival (1945–present) After the war, trams came to be seen as an outdated and inflexible form of transportation