If only the polluter were to pay the true price of his actions – so the theory goes – the level of polluting consumption would be reduced to a more optimal level.  How to solve this for cars is tackled in a new book called Critical Mass by Nick Molden (1992, PPE) together with Professor Felix Leach of Keble College.

As soon as you move from theory to practice, quantifying the environmental impact gets highly complex, and controversial. Critical Mass, published by the Society of Automotive Engineers in October 2024, aims to resolve this through radical simplification in the style of Occam’s razor. The crucial question they ask is: If you could know only one piece of information to estimate the total environmental impact of your vehicle, and to compare between vehicles, what would it be?

The resulting answer is car weight. Eighty-three percent of unabated pollutants they show to be linked to vehicle mass. It sets up the opportunity to replace the complex web of vehicle taxation with a simple charge based on the car’s weight and annual distance driven – in doing so, taxation would then align with environmental damage.

In short, Critical Mass contains is powerful new thinking to tax pollution, fix declining car tax revenues and simplify car choices.