trams rapidly became very popular; by 1903, there were 300 electric tramcars in London, which carried 800,000 passengers over Whitsun weekend in 1903. The London County Council Tramways first electric line opened in May 1903 between Westminster Bridge and Tooting and the LCC sold 3.3 million tickets in its third year of business or five times the traffic carried by its horse trams. The LCC saw the electric trams as a way of driving social change, as its cheap, fast service could encourage workers to move out of the crowded inner city and live healthier lives in the suburbs. Soon other London boroughs introduced their own electric services, including West Ham, Leyton, Dartford and Bexley. Although the City of London and the West End of London never gave permission for tram lines to be built, trams were allowed to use the Victoria Embankment and cross the Thames over Westminster and Blackfriars Bridges; on 14 September 1909, Lord Mayor George Wyatt Truscott opened the widened Blackfriars Bridge and drove the first tram across it. By 1914, the London tram operators formed the largest tram network in Europe but the onset of the Great War saw a halt in the expansion of the trams and thousands of conductors left to join the armed forces to be replaced by "substitute" women conductors known as 'conductorettes' (A tram driver, like an omnibus driver, was deemed as a reserved occupation as it was considered that women did not have the physical capability of operating the heavy electrical controller or the brakes). Several different companies and municipalities operated London's electric tramways. The largest was the LCC, with lines equipped with conduit current collection. Other operators mainly used the more conventional overhead electric wires. Many of London's trams had to be equipped with both systems of electricity supply, with routes being equipped with change points. During their heyday, tram services covered much of inner London and reached out to the suburbs, assisted by facilities like the Kingsway tramway subway, which enabled the longest tram route entirely within the County of London to operate: a weekend service between Archway, then part of Highgate, and Downham via Brockley, . Route coverage might have been wider still but the terms of the 1870 Act meant that the passage of new tramways had to be negotiated individually with local authorities, who would sometimes impose prohibitively expensive improvement works as a condition