We assemble a new global database on motor vehicle travel speed in over 1,200 large cities in 152 countries. We then estimate comparable city-level indices of travel speed and congestion. Most of the variation in urban travel speed is across countries, not within. National income per capita explains most of this cross-country variation in speed. In rich countries, urban travel is roughly 50% faster than in poor countries. To investigate the link between economic development and mobility, we develop an urban model with endogenous travel, road infrastructure, and land area. The model provides an exact decomposition of how city size, infrastructure, and topography contribute to explaining why urban travel is faster in richer countries. We find that richer countries are faster, mainly because their cities have more major roads and wider land areas. These effects operate by increasing uncongested speed, not by reducing congestion.