The road from Kampala, the capital of Uganda, to Jinja, the site of Africa’s first electric bus factory, was packed with cars on a July morning. The traffic crawled. Breathing hurt your throat. Kampala was the most polluted city in the world that day, according to OpenAQ, a global air pollution tracker, and much of that was due to vehicle fumes. The journey was a lesson in why it’s so necessary — and also so challenging — to move the continent’s vehicles away from petrol and diesel.