London introduced congestion pricing over 20 years ago to tackle some of the world's worst traffic. Today, on average, drivers still spend 101 hours a year stuck in gridlock – so why is the once-controversial £15 daily charge more popular than ever?

While the charge hasn't eliminated congestion, and it's made an expensive city even more expensive, it has quietly transformed London in other ways: funnelling over £2.6 billion into public transport improvements and reducing air pollution.