Like many Australian cities, Melbourne has a high dependency on the automobile for transport, particularly in the outer suburban areas where the largest number of cars are bought, with a total of 3.6 million private vehicles using 22,320 km (13,870 mi) of road, and one of the highest lengths of road per capita in the world. The early 20th century saw an increase in popularity of automobiles, resulting in large-scale suburban expansion. By the mid 1950s there was just under 200 passenger vehicles per 1000 people by 2013 there was 600 passenger vehicles per 1000 people. Today it has an extensive network of freeways and arterial roadways used by private vehicles including freight as well as public transport systems including bus and taxis. Major highways feeding into the city include the Eastern Freeway, Monash Freeway and West Gate Freeway (which spans the large West Gate Bridge), whilst other freeways circumnavigate the city or lead to other major cities, including CityLink (which spans the large Bolte Bridge), Eastlink, the Western Ring Road, Calder Freeway, Tullamarine Freeway (main airport link) and the Hume Freeway which links Melbourne and Sydney.