High-occupancy vehicle lanes are intended to both speed traffic and improve air quality. This is done by dedicating a lane to cars with two or more occupants, thus reducing the number of vehicles traveling on the road. This both speeds traffic flows and reduces pollution. Some have argued, however, that if underutilized, such lanes can create congestion.
Between 1950 and 1990, while the population of U.S. metropolitan areas grew 72%, the central cities shrank by 17%. Factors that could account for central cities’ population decline include faster commutes, population sorting due to racial and social preferences and perceived increases in city crimes.
Once part of the urban fabric of the United States, streetcars declined as the automobile rose during the 1930s and 1940s. In the last several decades, however, streetcars have returned to popularity — more than 40 new systems are in planning, construction or operation.
