the increased use of elevators in residential buildings, were the impetus behind a new housing code that effectively ended the tenement as a form of new construction, though many tenement buildings survive today on the East Side of the borough. Conversely, there were also areas with luxury apartment developments, the first of which was the Dakota on the Upper West Side. Manhattan offers a wide array of public and private housing options. There were 852,575 housing units in 2013 at an average density of 37,345 per square mile (14,419/km²). , only 20.3% of Manhattan residents lived in owner-occupied housing, the second-lowest rate of all counties in the nation, behind the Bronx. Although the city of New York has the highest average cost for rent in the United States, it simultaneously hosts a higher average of income per capita. Because of this, rent is a lower percentage of annual income than in several other American cities. Manhattan's real estate market for luxury housing continues to be among the most expensive in the world, and Manhattan residential property continues to have the highest sale price per square foot in the United States. Manhattan's apartments cost , compared to San Francisco housing at , Boston housing at , and Los Angeles housing at . Infrastructure Transportation Public transportation Manhattan is unique in the U.S. for intense use of public transportation and lack of private car ownership. While 88% of Americans nationwide drive to their jobs, with only 5% using public transport, mass transit is the dominant form of travel for residents of Manhattan, with 72% of borough residents using public transport to get to work, while only 18% drove. According to the 2000 United States Census, 77.5% of Manhattan households do not own a car. In 2008, Mayor Michael Bloomberg proposed a congestion pricing system to regulate entering Manhattan south of 60th Street. The state legislature rejected the proposal in June 2008. The New York City Subway, the largest subway system in the world by number of stations, is the primary means of travel within the city, linking every borough except Staten Island. There are 151 subway stations in Manhattan, out of the stations. A second subway, the PATH system, connects six stations in Manhattan to northern New Jersey. Passengers pay fares with pay-per-ride MetroCards, which are valid on all city buses and subways, as well as on PATH trains. There are 7-day