[1] The complexity of the Belgian political landscape makes some transportation issues difficult to solve.[2] The Brussels tram system evolved a lot over time, from a rise in the first half of the 20th century (246 km (153 mi) of tram rails were serviced in 1955)[3] to a fall in the second half of the 20th century due to the popularisation of transport by bus and by car.[5] The Infrabel railway network has a total of eight lines used by passenger trains, which lie partly of completely within the region of Brussels.The most notable is Brussels Airport, located in the nearby Flemish municipality of Zaventem, 12 km (10 mi) east of the capital, which can be accessed by highway (A201), train and bus.The secondary airport is Brussels South Charleroi Airport, located in Gosselies, a part of the city of Charleroi (Wallonia), some 50 km (30 mi) south-west of Brussels, which can be accessed by highway (E19 then E420) or a private bus.Brussels is characterised by a relatively low level of cycling compared to Flanders and many other north-western European cities.