Roads are the arteries through which the economy pulses. By linking producers to markets, workers to jobs, students to school, and the sick to hospitals, roads are vital to any development agenda. Since 2002, the World Bank has constructed or rehabilitated more than 260,000 km of roads. It lends more for roads than for education, health, and social services combined. However, while roads bring economic and social benefits, they can also come with social costs such as pollution or deforestation. The Amazon rainforest is crisscrossed by almost 100,000 km of roads—enough to circle the Earth two and a half times. And the transport sector accounts for about 23 percent of global energy-related carbon dioxide emissions and a significant share of local particle pollution. Such tradeoffs need to be weighed when planning any intervention.