Outside the US, there are many examples (Japan and China both do this). In the US, I don't know specific examples, but you can definitely use a combination of

Outside the US, there are many examples (Japan and China both do this). In the US, I don't know specific examples, but you can definitely use a combination of policies (building public transit, zoning laws to encourage high density, making parts of the city more pedestrian-friendly - and generally less car-friendly) to encourage high density.