In the urban planning literature, it is frequently explicitly asserted or strongly implied that ongoing urban sprawl and decentralization can lead to development patterns that are unsustainable in the long run. One manifestation of such an outcome is that if extensive road investments occur, urban sprawl and decentralization are advanced and locked-in, making subsequent investments in public transit less effective in reducing vehicle kilometers traveled by car, gasoline use and carbon dioxide emissions. Using a simple core-periphery model of Beijing, the authors numerically assess this effect. The analysis confirms that improving the transit travel time in Beijing s core would reduce the city s overall carbon dioxide emissions, whereas the opposite would be the case if peripheral road capacity were expanded. This effect is robust to perturbations in the model s calibrated parameters. In particular, the effect persists for a wide range of assumptions about how location choice depends on travel time and a wide range of assumptions about other aspects of consumer preferences.