Transportation is the biggest producer of carbon emissions for many people, and the reason for this is that most cities are not easily accessable by walking or biking. This raises the question about what a sustainable city would look like. A sustainable city with low carbon emissions would offer multiple methods of transportation including busses, a subway system, and the ability to walk or bike from place to place. However, cities that do not have the virtue of walkability will most likely stay that way. A city that is already built cannot change its layout, and it would take many years to develop and build a subway system that goes throughout the whole city. While it is unlikely for these methods of transportation to be in service anytime soon for most cities, there is an alternative. Carpooling is one thing that everyone can do to help reduce their carbon emissions. The link below is a commercial about carpooling. It says that if everyone carpooled for just one day a week, we could save enough gas to fill one million tanker trucks. Just imagine what we could do if we carpooled everyday!