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18 Higher-Density Development <br />MYTH THREE FACTTHREE <br />With a typical family now making more car trips for family, personal, social, and <br />recreational reasons than for commuting to work,27 reducing the number of <br />noncommuting trips takes on greater importance in the battle to reduce traffic <br />congestion and parking problems. A case study in Washington, D.C., found that <br />workers in dense downtown Washington made 80 percent of their mid-day trips <br />by foot while suburban workers made 67 percent of their mid-day trips by car.28 <br />Although a suburban office park would never reach the density levels of a down- <br />town area, planners can still reduce the auto dependency of suburban office work- <br />ers by using some of the same design techniques. Concentrating density around <br />suburban offices, allowing and encouraging retail and restaurants in and near <br />the offices, and planning for pedestrian and bike access can all reduce the <br />number of lunchtime car trips required by office workers. <br />Higher-density mixed-used developments also create efficiencies through shared <br />parking. For example, office and residential uses require parking at almost exact <br />opposite times. As residents leave for work, office workers return, and vice versa. In <br />addition, structured parking becomes feasible only with higher-density developments. <br />Higher-density development also makes public transit more feasible. When a com- <br />munity that includes residences, shops, and offices reaches a certain threshold of <br />density, public transit-shuttles, bus service, trams, or light rail becomes an option <br />for residents. It is estimated that a minimum density of seven dwelling units per <br />acre is needed to make local bus service feasible with an intermediate level of <br />service.29 Light rail needs a minimum density of nine dwelling units per acre to <br />be feasible.30 When a community can take advantage of these options and increase <br />the transportation choices for residents, relief is greater as total car dependency is <br />further broken. Such choices are impossible for low-density developments. <br />AVERAGE DAILY CAR TRIPS <br />NUMBER OF TRIPS DAILY <br />10 <br />8 <br />6 <br />4 <br />2 <br />0 <br />Apartment <br />6.3 <br />Single-Family <br />Detached <br />10.0 <br />TYPE OF HOUSING <br />Source: Institute of Traffic Engineers,Trip Generation,6th Edition, vol. 1 (Washington, D.C.: Author, 1997).