Many people assume that at lower speeds extra fuel is used and more pollution created. In fact the reverse is true. That’s why "Total 20", without traffic calming, is supported by so many environmental organisations.
Far from being anti-motorist, 20 mph limits give drivers many advantages. That’s why 72% of drivers believe 20’s Plenty on residential streets.
 National Centre for Social Research, British Social Attitudes: the 22nd Report, 2005