Houston is considered an Automobile dependency city, with an estimated 77.2% of commuters driving alone to work in 2016, up from 71.7% in 1990 and 75.6% in 2009. In 2016, another 11.4% of Houstonians carpooled to work, while 3.6% used public transit, 2.1% walked, and 0.5% bicycled. A commuting study estimated that the median length of commute in the region was  in 2012. According to the 2013 American Community Survey, the average work commute in Houston (city) takes 26.3 minutes. A 1999 Murdoch University study found that Houston had both the lengthiest commute and lowest urban density of 13 large American cities surveyed, and a 2017 Arcadis study ranked Houston 22nd out of 23 American cities in transportation sustainability. Harris County is one of the largest consumers of gasoline in the United States, ranking second (behind Los Angeles County, California) in 2013.. What commuters made up the largest percentage of the population?