The issue of automobile pollution in cities get highlighted the most in Delhi which has by far the largest number of cars and two-wheelers and which provides a foretaste of the blight that is likely to visit other urban centres in good time. Controling vehicular pollution is a complicated issue and involves better traffic management, urban planning, public transportation systems, improving fuel quality and roads, and enforcement of better emission norms.There is also a petrol verus diesel issue and debates about whether catalytic convertors and unleaded petrol have indeed helped. For example, there is argument that unleaded petrol reduces lead emissions, but increase benzene.