If we're talking about transportation, the best thing a city can do is densify as quickly as it can. That needs to be said every time this issue comes up, because it's the only universal strategy that works.
In tough times, some of us see protecting the climate as a luxury, but that's an outdated 20th-century worldview from a time when we thought industrialization was the end goal, waste was growth, and wealth meant a thick haze of air pollution.