When the City of London Corporation evaluated a city-wide 20mph limit they commissioned the respected Imperial College London to evaluate emissions effects[1]. They found that for diesel vehicles there is a substantial reduction in harmful Nitrogen Oxides (NOx) and Particulates (PM₁₀) emissions from implementing 20mph limits. Key figures are:-

In 2014, 37% of cars on UK roads were diesels[3]. Where a 20mph limit is implemented the reduction in total NOx and PM₁₀ emissions is large enough to be the equivalent of taking nearly half of the 63% petrol cars off the roads.

20mph limits therefore provide a significant reduction in the most toxic emissions for built-up roads so assisting local authority compliance with legal air quality requirements and reducing premature air quality related deaths.

Rod King MBE, Founder and Campaign Director of 20’s Plenty for Us said:-

“Many UK cities break legal NOx and PM₁₀ pollution levels, killing people early and risking fines. A 20mph built up limit simply, immediately and effectively reduces dirty fumes. This government should urgently wake up to the air quality gains from 20mph.  Lower speeds give so many road safety, active travel and public health benefits. The government should stop hiding behind the fig-leaf of “localism” on speed limits and immediately cut the requirement for, and costs of, 20mph repeater signs.  Then change the national limit from 30mph to 20mph letting local authorities decide where a higher speed limit is appropriate taking full account of all their public health responsibilities.[4]”