Should you pay to drive into your city centre — for the sake of the climate?

Authorities in New York city are planning to introduce a congestion pricing scheme. Vehicles entering certain parts of Manhattan will soon have to pay for the right to do so. Proponents of such schemes say they help reduce traffic, improve air quality, and can boost public transport patronage and funding. But from the experience of other cities around the world, vested interests and partisan politics can prove a stumbling block. So, what measures work best and how do you ensure social and economic equity?