Unfortunately, sufficient housing opportunities and transportation choices are currently lacking from many of our great urban areas to achieve these efficiencies. Luckily, there are numerous places to look to and learn from as we make our urban areas more desirable and livable. Many European countries have made different choices about about how to set up their transportation systems and that is one of the reasons why their per capita CO2 emissions in the transportation sector are much lower than in the US. Thus, the environmental challenge for our cities is how to provide more small homes and more opportunities for walking while also making them more livable with good schools, parks, healthy food, safe streets and economic opportunity.