Citation(s) from the GunPolicy.org literature library
Renner, Michael. 2008 ‘Vehicle Production Rises, But Few Cars Are 'Green'.’ Vital Signs Online: Transportation and Communication. Washington, DC: Worldwatch Institute. 21 May
The world's fleet of passenger vehicles is now an estimated 622 million, up from 500 million in 2000 and a mere 53 million in 1950.