Switzerland has a dense network of roads and railways. The Swiss public transport network has a total length of 24,500 kilometers and has more than 2600 stations and stops. The crossing of the Alps is an important route for European transportation, as the Alps separate Northern Europe from Southern Europe. Alpine railway routes began in 1882 with the Gotthard Railway with its central Gotthard Rail Tunnel, followed in 1906 by the Simplon Tunnel and the Lötschberg Tunnel in 1913. As part of the New Railway Link through the Alps (NRLA) in 2007 the Lötschberg Base Tunnel opened and in 2016 the Gotthard Base Tunnel opened on 1 June. The Swiss road network is funded by road tolls and vehicle taxes. The Swiss motorway system requires the purchase of a road tax disc - which costs 40 Swiss francs for one calendar year - in order to use its roadways, for both passenger cars and trucks. The Swiss motorway network has a total length of 1,638 kilometres (as of 2000) and has also - with an area of 41,290 km2 - one of the highest motorway densities in the world. Zurich Airport is Switzerland's largest international flight gateway, handling 24.9 million passengers in 2013. The second largest airport, Geneva Cointrin, handled 14.4 million passengers (2013) and the third largest EuroAirport Basel Mulhouse Freiburg 6.5 million passengers; both airports are shared with France. Switzerland has approved billions of francs for the improvement of its public transportation infrastructure. The modal split for public transportation is one of the highest in Europe, standing at 21.3% in 2010. In many cities with a population above 100,000, the modal split for public transportation lies above 50%. Railways Switzerland has a very high density of railway network, with an average of 122 km of track for every 1,000 km2 (average of 46 km in Europe). In 2008, each Swiss citizen traveled, on average, 2,422 km by rail, which makes them the most frequent users of rail transport. Many of the Swiss standard gauge railway lines are part of the nationwide Swiss Federal Railways system, although other standard gauge lines are operated by independent companies such as BLS AG. In addition numerous narrow gauge railways are operated, the largest company of its kind being the Rhaetian Railway. In total 5,100 km of rail network are used. The Swiss Federal Railways run some 5000 passenger train services covering about