car phenomenon, demonstrating that economic and sociodemographic factors account for most or all of the observed slowdowns. Recent statistics in the US show total vehicle-miles traveled (VMT) increasing after several years of decline, although per-capita VMT remains below its all-time high. Proposed causes There is speculation about causes of a decline in automobile usage. Analysts such as Newman as well as views expressed in the journal edited by Melia entitled World Transport Policy and Practice point to various interrelated causes. Factors include: Travel time budgets, a theoretical psychological limit suggesting a long term constraint on the amount of time people allocate to travel of about one hour a day. Studies using this concept (albeit not always defined in the same way) have included those of Zahavi (1974), Mogridge (1983) and Metz (2010) who suggested that saturation would naturally follow from the observation that access to destinations increased with the square of speed, but was offset by the tendency for each additional choice of destination to offer less and less extra benefit. A version was suggested by Marchetti, sometimes called 'the Marchetti Wall'; when cities become more than "one hour wide," they stop growing or they become dysfunctional, or both. The growth of public transport. For example, railway travel in the United Kingdom has been undergoing a renaissance, according to one view. In the US Amtrak has posted record ridership for every year since 2000 with the exception of 2009. The reversal of urban sprawl and other population shifts from suburbs to cities. The growth of a culture of urbanism. The ageing of cities, especially their road infrastructure, much of which is at or near the end of its intended life. Rising fuel prices. Increasing costs of automobile ownership, including costs for insurance and parking. Traffic-reducing policies such as the "pedestrianisation" of city centres, traffic calming, parking control, congestion charging. Proliferation of different ways to own and hire vehicles, such as Streetcar, Zipcar, and Whipcar, as well as other options for car sharing. Reallocation of road capacity away from cars towards bikes and pedestrian traffic resulting in disappearing traffic. Cultural shifts especially among young people for whom acquisition of a driving licence is now seen less as a key rite of passage into adulthood, and is reflected in recent reductions in the propensity of young people to acquire driving licences. One report suggests there has been a shift in notions about