Many governments commit significant portions of their budgets to building and maintaining transportation infrastructure. For example, nearly 20 percent of the money lent from the World Bank to developing countries is earmarked for transportation infrastructure projects, which is more than education, health and social services combined. Some of these projects, such as the Interstate Highway System in America or the National Trunk Highway System in China, are breathtaking achievements of engineering. But the costs of projects like these are also breathtaking, and their economic benefit is often unclear. Recent research finds that the economic benefits of transportation infrastructure investment can be significant.