For decades, a sizeable proportion of America’s car makers have resisted the pressure to improve the fuel efficiency of their beloved gas guzzlers – and we've been treated to a succession of fantastically loud, extremely powerful, not-especially-green-but-heroically-mean machines as a result; cars such as the Corvette, the Trans Am and the Dodge Charger; and more recently the Viper, the Mustang GT500 and a whole raft of SUVs, pick-ups and the like.

As of 2025, however, the days of such cars would appear be over.

The average fuel consumption for an American car at the moment is approximately 29mpg, but that will need to rise to a heady 54.5mpg by 2025 now that President Obama has signed his country’s car makers up to a sweeping new industry agreement on fuel efficiency. And Detroit, it seems, is well on board.