the city. Milan road system is characterized by a high rate of traffic congestion, due to a high level of cars per capita and a high number of commuters in the metropolitan area. Congested traffic is also responsible for the high pollution rate in the Milan area. Counter measures included the partial ban of private cars inside the Milan urban area for some period, usually during Sundays. In 2008, a traffic pollution charge for vehicles entering the city, Ecopass, was introduced. The program resulted in a lower proportion of highly polluting vehicles on the roads in the city. However, the program progressively lost effectiveness as the city's vehicle fleet got greener. Since 16 January 2012 a new program, Area C, was introduced as a congestion charge (as opposed to the previous pollution charge), thus targeting any private vehicle entering Milan city center. Although high by European standards, Milan is one of the big cities with the lowest number of motor vehicles per capita in Italy, with 543 per 1000 people in 2011. Car sharing Several car-sharing systems are active in the city. GuidaMi, the first scheme, is managed by ATM and comprises 132 vehicles and about 5,500 registered users. Car2go was activated in August 2013 and has a fleet of 700 cars and more than 50,000 registered users. Other services include E-vai from Trenord, DriveNow from BMW, Twist and Enjoy from Eni. In 2015 the Chinese automaker ZD introduced its Sharen'go electric car-sharing service to Milan, making it the first city outside the company's native China where the service was available. Car sharing in Milan serves about 0.5% of the total mobility of the city, and with 323,000 users, as of June 2016 it is the Italian city with the largest number of car sharing customers. Cycling The city's mostly flat topography favors cycling. The cycle routes network is still limited, but is being constantly expanded. Milan was also one of the first Italian cities to activate a bike sharing system. Airports Milan's airport system is the second busiest in Italy, after that of Rome. The city is served by three major airports: Malpensa Airport, the biggest in northern Italy; Linate Airport, located near the city centre and mainly used for domestic traffic; and Orio al Serio Airport, located in the neighbouring city of Bergamo, used mainly by low-cost airlines. Combined, these three airports transported a total of 43 million