Since 2009, the United States is home to the second largest passenger vehicle market of any country in the world, second to China. Overall, there were an estimated 263.6 million registered vehicles in the United States in 2015, most of which were passenger vehicles. This number, along with the average age of vehicles, has increased steadily since 1960. The United States is also home to three large vehicle manufacturers: General Motors, Ford Motor Company, and Chrysler, which have historically been referred to as the "Big Three". Cars became popular in the U.S. after the introduction of the Ford Model T in 1908, and experienced a further increase in popularity after the construction of the Interstate Highway System and the suburbanization of the United States in the 1950s. In the 21st century, large SUVs have become popular in the U.S., leading to increased greenhouse gas emissions and pedestrian deaths. The National Highway Traffic Safety Administration writes and enforces the Federal Motor Vehicle Safety Standards. The United States is commonly regarded as a car-centric country, with cars being a dominant American mode of transport. U.S. infrastructure and road rules tend to privilege cars over other road users such as cyclists and pedestrians. Cars have been a major component of American culture, particularly since the 1950s. Statistics The United States Department of Transportation's Federal Highway Administration as well as the National Automobile Dealers Association have published data in regard to the total number of vehicles, growth trends, and ratios between licensed drivers, the general population, and the increasing number of vehicles on American roads. Overall passenger vehicles have been outnumbering licensed drivers since 1972 at an ever-increasing rate, while light trucks and vehicles manufactured by foreign makes have gained a larger share of the automotive market in the United States. In 2001, 70% of Americans drove to work in cars. New York City is the only locality in the country where more than half of all households do not own a car (the figure is even higher in Manhattan, over 75%; nationally, the rate is 8%). Total number of vehicles There are two types of sources for vehicle registration data, known as Vehicles in Operation (VIO): governmental sources such as the Bureau of Transportation Statistics and Federal Highway Administration (FHWA), and commercial, for-profit companies such as IHS and Hedges & Company. According to the Bureau of Transportation Statistics for 2012, there were 254,639,386