polluting vehicles will be charged to drive through the city centre. The Clean Air Zone is currently due to come into effect in Summer 2022. Green belt The city has green belt mainly along its southern fringes, taking in small areas within the Ashton Court Estate, South Bristol crematorium and cemetery, High Ridge common and Whitchurch, with a further area around Frenchay Farm. The belt extends outside the city boundaries into surrounding counties and districts, for several miles in places, to afford a protection from urban sprawl to surrounding villages and towns. Demographics In 2014, the Office for National Statistics estimated the Bristol unitary authority's population at 442,474, making it the 43rd-largest ceremonial county in England. The ONS, using Census 2001 data, estimated the city's population at 441,556. According to the 2011 census, 84% of the population was White (77.9% White British, 0.9% White Irish, 0.1% Gypsy or Irish Travellers and 5.1% Other White); 3.6% mixed-race (1.7% white-and-black Caribbean, 0.4% white-and-black African, 0.8% white and Asian and 0.7% other mixed); 5.5% Asian (1.6% Pakistani, 1.5% Indian, 0.9% Chinese, 0.5% Bangladeshi, and 1% other Asian); 6% Black (2.8% African, 1.6% Caribbean, 1.6% Other Black), 0.3% Arab and 0.6% with other heritage. Bristol is unusual among major British towns and cities in its larger black than Asian population. These statistics apply to the Bristol Unitary Authority area, excluding areas of the urban area (2006 estimated population 587,400) in South Gloucestershire, Bath and North East Somerset (BANES) and North Somerset—such as Kingswood, Mangotsfield, Filton and Warmley. 56.2% of the 209,995 Bristol residents who are employed commute to work using either a car, van, motorbike or taxi, 2.2% commute by rail and 9.8% by bus, while 19.6% walk. Inequality The Runnymede Trust found in 2017 that Bristol "ranked 7th out of the 348 districts of England & Wales (1=worst) on the Index of Multiple Inequality." In terms of employment, the report found that "ethnic minorities are disadvantaged compared to white British people nationally, but this is to a greater extent in Bristol, particularly for black groups." Black people in Bristol experience the 3rd highest level of educational inequality in England and Wales. Bristol conurbation The population of Bristol's contiguous urban area was put at 551,066 by the ONS based on Census 2001 data. In 2006 the ONS estimated Bristol's urban-area population at 587,400, making it England's sixth-most populous city and tenth-most populous urban area.