Outdoor air pollution kills more than three million people across the world every year, and causes health problems from asthma to heart disease for many more. This is costing OECD societies plus People’s Republic of China and India an estimated USD 3.5 trillion dollars a year in terms of the value of lives lost and ill health, and the trend is rising. But how much of the cost of those deaths and health problems is due to pollution from cars, trucks and motorcycles on our roads? Initial evidence suggests that in OECD countries, road transport is likely responsible for about half the USD 1.7 trillion total.