Complex sentence: A second and more extensive network was approved in 1945, when it was decided to gradually replace trams with trolleybuses, preferred for being more manoeuvrable and "more modern", and preferred over diesel or petrol buses due to better traction on steep slopes.
Split into simpler sentences: A second and more extensive trolleybus system was approved in 1945, when it was decided to gradually replace the city's trams with trolleybuses. Trolleybuses were preferred over trams for being more manoeuvrable and "more modern", and were preferred over diesel or petrol buses due to better traction on steep slopes.