Established alternatives for some aspects of automobile use include public transit such as buses, trolleybuses, trains, subways, tramways light rail, cycling, and walking. Car-share arrangements and carpooling are also increasingly popular–the US market leader in car-sharing has experienced double-digit growth in revenue and membership growth between 2006 and 2007, offering a service that enables urban residents to "share" a vehicle rather than own a car in already congested neighborhoods.^[49] Bike-share systems have been tried in some European cities, including Copenhagen and Amsterdam. Similar programs have been experimented with in a number of US Cities.^[50] Additional individual modes of transport, such as personal rapid transit could serve as an alternative to automobiles if they prove to be socially accepted.^[51]