20’s Plenty is green

It’s a popular misconception that fuel efficiency peaks at 50-60mph. However, What Car magazine found that for many cars 20mph was the most efficient speed.  In urban conditions 20mph beats 30mph for saving fuel. 20mph limits mean less acceleration and braking. Walking and cycling increase. 

Britain suffers from excessive speeds and volumes of motorised traffic, which affects our environment, climate and health. Traffic brings pollution, congestion, noise and degrades the built environment. Road transport contributes one-fifth of the UK's total emissions of carbon dioxide (CO₂), the main greenhouse gas. Road transport CO₂ increased nearly 23% between 1990 and 2010. Transport is the only sector where greenhouse gas emissions are rising.

When 30km/h (18.6mph) zones were introduced in Germany, car drivers changed gear 12% less often, braked 14% less often and required 12% less fuel. This implies 20mph limits without humps can cut residential transport emissions by 12%. Traffic smoothes, gaps between cars shorten, it’s easier to merge and there’s less idling with dangerously concentrated pollutants. Limits either speed up trip times due to smoother traffic, or do not significantly affect times from origin to destination. 

Some people are afraid to walk or cycle.  20mph limits improve fairness in sharing the public space of roads between vulnerable users and traffic. Bristol found 20mph increased walking 23% and cycling 20.5%. Traffic reduction could cut another 5-10% of fuel use.  This all helps drivers to save money, reduce pollution and conserve our dwindling reserves of liquid fuels like oil and diesel.

With 20mph limits it’s easier and safer to reach local amenities. This helps keep nearby shops viable - with important accessibility and mixed use planning benefits.  20mph supports local facilities and jobs in the face of competition from edge of town developments or e-shopping. Those without a car, the elderly, disabled, families or on foot or cycling are more likely to frequent and enjoy local and convenience stores for longer, strengthening their community and making their lives more sustainable and resilient.

20mph is up to 40% quieter than 30mph, making urban areas more pleasant. People can more easily talk and play outside which raises health and neighbourliness and reduces crime. An additional eco benefit includes less need for road signage lighting as this is not required on many warning signs in a 20mph limit.

Environmental groups supporting wide 20mph limits include: Friends of the Earth; CPRE; Campaign for Better Transport; The Conservation Volunteers; Environmental Protection UK; Chartered Institute of Environmental Health; CTC the national cyclists’ organisation; Environmental Association for Universities and Colleges; Ramblers’ Association; Sustainable Development Commission; ETA Trust; Transform Scotland; Sustrans; Living Streets; The Liberal Democrat and Green Parties; Stockholm Environment Institute and more.

A 20’s Plenty for Us Briefing, October 2012.