working-class suburbs, and by the turn of the century, most Northern towns had an extensive interconnected electric tram network. At the network's height, it was possible to travel entirely by tram from Liverpool Pier Head to the village of Summit, outside Rochdale, a distance of , and a gap of only separated the North-Western network from the West Yorkshire network. Starting in the 1930s, these were largely replaced by motor buses and trolley buses. With the closure of Sheffield Tramway in 1960 and Glasgow Tramway in 1962, Blackpool Tramway – popular as a tourist attraction as much as a means of transport – was left as the only public tram system in the UK until the Manchester Metrolink opened in 1992. Today there are four light rail systems in the North – Blackpool Tramway, Manchester Metrolink, Sheffield Supertram and Tyne & Wear Metro. Air Manchester Airport serves as the main international hub for Northern England and is the busiest airport anywhere in the UK outside London, handling 27.8 million people in 2017. In total, there are eight international airports in the North; these are (in descending order of passenger traffic) Manchester, Newcastle, Liverpool John Lennon, Leeds Bradford, Doncaster Sheffield, Humberside, Teesside and Carlisle Lake District. Many of these airports were developed during the boom in low-cost air travel during the early 2000s, but have suffered since the Great Recession – Teesside is running at just 3% of its maximum capacity, and Blackpool Airport closed as an international airport in 2014. The devolution of Air Passenger Duty to Scotland represents a further possible threat to Northern English airports, allowing Scottish airports to offer cheaper flights than their English rivals. Few spoke flights operate between Northern airports and the national hubs at Heathrow and Gatwick, putting further strain on the smaller Northern airports and forcing connecting passengers to travel via continental European airports. The planned High Speed 2 station at Manchester Airport will offer direct high-speed services to London, allowing spare capacity at Manchester Airport to take some of the flights which currently serve busy London airports. Water The first modern canal in England was Sankey Brook, opened in 1757 to connect Liverpool's ports to the St Helens coalfields. By 1777, the Grand Trunk Canal had opened, linking the rivers Mersey and Trent and making it possible for boats to travel directly from Liverpool on the west coast to Hull on the