Combined with the fact that many automobile trips are made with a single occupan t in the vehicle, the automobile is a very inefficient means of urban transportation, using far more energy, and emitting far more CO2 and other pollutants per passenger mile traveled than other alternatives. Car pools are another way to reduce transportation energy use and CO2 emissions. A c ar with four passengers uses only about one quarter of the fuel of four SOVs. The most fuel efficient forms of transportation with respect to energy use and CO2 emissions are non-mechanized modes such as walking and bicycling. As well as resulting in extremely low net emissions of any pollutants, walking and cycling can provide healthy exercise.
Municipalities have a great deal of control over the transportation systems within their boundaries.
Land use planning which promotes compact development without the typical sprawl of recent automobile-dependent suburbs is one way that cities can reduce the number of miles inhabitants must travel. Public transit is more economical and convenient i n areas with higher population densities. If municipalities are zoned to permit mixed residential and commercial uses, it is much more likely that people can walk or cycle to work or to shop. Comparisons of cities around the world show a clear link between urban population density and gasoline consumption. As well as being responsible for roads, municipalities often run local public transit systems, and as such can exert a great influence over the cost and convenience of transit compared to that of the automobile.