In the midst of the second world war, the US government warned: “When you ride alone, you ride with Hitler.” The 1943 propaganda poster by Weimer Pursell urged Americans to car-pool to conserve petrol. In 2002, Bill Maher, the politically opinionated comedian revived the poster – and the theme – in a book he called: When You Ride Alone You Ride With Bin Laden.

His timing was auspicious. Since 2002 oil prices have risen dramatically, reaching a record of $147 a barrel in July – 15 times what it was a decade before. As oil prices rose because supply was unable to keep up with booming demand from China and elsewhere, petrol prices followed. Costs grew so dramatically that European truckers organised mass strikes, American drivers abandoned their petrol-guzzling sports utility vehicles, and car pooling began to stage a comeback.