According to the United Kingdom Census 2011, 84% of the population was White people (77.9% White British, 0.9% Irish migration to Great Britain, 0.1% Gypsy (term) or Irish Travellers and 5.1% Other White); 3.6% Mixed (United Kingdom ethnicity category) (1.7% white-and-black Caribbean, 0.4% white-and-black African, 0.8% white and Asian and 0.7% other mixed); 5.5% British Asian (1.6% British Pakistanis, 1.5% British Indian, 0.9% British Chinese, 0.5% British Bangladeshi, and 1% other Asian); 6% Black British (2.8% African, 1.6% British African-Caribbean people, 1.6% Other Black), 0.3% British Arabs 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.
Question: What is the least common method of transportation for Bristol residents?
Answer: rail