Summary

Urbanization is a central challenge of our times. At its core, it is an urban development challenge that requires addressing transportation and housing in cities. Transport improvements can reduce travel times and improve the spatial reach of urban dwellers. But these improvements may be crowded out by latent demand for travel and may lead to worse congestion, pollution, and other negative externalities associated with urban traffic. To evaluate the effects of transport improvements, direct travel effects must be measured. Then, an improvement in traffic conditions somewhere may spill over to other areas. Firms and residents may also relocate, so economic growth close to a transport improvement may just result from a displacement of economic activity from other areas. Conversely, better accessibility is expected to foster agglomeration effects and increase productivity. Valuing these changes is difficult, as it requires being able to quantify many externalities such as congestion delays, scheduling gains, and greater job accessibility. Housing policies present different challenges. More fundamental policies seek to enable housing construction by offering more secure property rights, up-to-date land registries, and competent land-use planning—all complex endeavors and all necessary. Other housing policies rely on heavy government interventions to provide housing directly to large segments of the urban population. These policies often flop because governments fail to link housing provision with job accessibility and appropriate land-use planning. Housing is also an expensive asset that requires significant initial funding, while credit constraints abound in the urbanizing world. Policymakers also need to choose between small improvements to extremely low-quality informal housing, retrofitting modern housing in already-built urban areas, or urban expansion. All these options involve sharp trade-offs, subtle induced effects, and complex interactions with transport. All these effects are difficult to measure and challenging to value.