In a world of online outrage, evidence is no longer enough – for a policy to work, politicians must explain it and stick by itImagine you’re a politician running a country. In front of you there is a proposal that in just nine months would save your society more than £45m, prevent almost 500 people being killed or injured, make your residential areas more appealing places to live in and reduce car insurance premiums by an average of £50. Tempting, right?Still not convinced? It is also backed by multiple scientific studies and examples of where it has been enacted in other parts of the world. Better yet, it was in your manifesto at the last election, when you became easily the largest party in your parliament. It also has the universal support of all emergency services in your nation. This is the dream.Will Hayward is a Guardian columnist. He publishes a regular newsletter on Welsh politics Continue reading...