Sustainable transport must be sustainable in terms of both social and environmental impact. Transport systems worldwide account for around 20% to 25% of energy usage and carbon dioxide emissions. Decarbonising transport will be a key sustainability challenge.
( Image: by Adam Coppola Photography (2014), Floating bus stop with bus dexter seattle. Available at: https://www.flickr.com/photos/greenlaneproject/22541247970 )