Congestion is geographically concentrated in major metropolitan areas, as close to 80 percent of America's growth and economic development is concentrated in metropolitan areas. Traffic congestion has grown worse in many ways in the past 30 years-trips take longer, congestion affects more of the day and affects more personal trips and freight shipments, and trip travel times are more unreliable. According to AASHTO, travel on the National Highway System has increased fivefold over the past 60 years, from 600 billion miles driven per year to almost 3 trillion in 2009.4 Annual travel is expected to climb to nearly 4.5 trillion miles by 2050, even with aggressive strategies to cut the rate of growth to only 1 percent per year.5