As a hybrid-car owner and health researcher, I was very interested in "Invasion of the Green Machines" [May 9], about the strong demand for hybrid cars. I think you missed the mark, though, in describing the motivation of hybrid-car buyers. Although emotional factors and anticipated long-term financial savings may play a role in the demand for hybrids, I believe the key to their popularity is that they provide a simple and effective way for an individual to reduce both local air pollution and our country's dependence on Middle East oil. What could be more practical?