Sadiq Khan thinks 20mph will banish accidents and serious injuries on London’s roads. Obviously no bad thing if it does. But would you want to be hit by a bus doing 20? Nor would I. These people see things in simplistic terms. Tony Blair once repeated the lazy phrase, “speed kills”. No, it’s speed in the wrong hands, or inappropriate speed that kills. Speed is like fire. Can be good, can be bad. Instead of learning to drive by numbers, we should learn to drive by context (more on this at the Speed tab). The 20mph campaign is well funded, so maybe that’s why it’s made such headway. Or is it because it delivers a simple message, whereas understanding what is meant by context requires some thought?