In the years following World War II, President Miguel Alemán Valdés's (1946–52) full-scale import-substitution program stimulated output by boosting internal demand. The government raised import controls on consumer goods but relaxed them on capital goods, which it purchased with international reserves accumulated during the war. The government spent heavily on infrastructure. By 1950 Mexico's road network had expanded to 21,000 kilometers, of which some 13,600 were paved. Large-scale dam building for hydroelectric power and flood control were initiated, most prominently the Papaloapan Project in southern Mexico. In recent years, there has been a re-evaluation of such infrastructure projects, particularly their negative impact on the environment.