By Dan Shapley
If all this talk about the carbon footprint of the average summer vacation gives you a distinctly 21st century squeamishness about travel, take heart. Now you can rent hybrid gas-electric vehicles from two of the nation's largest rental companies, at least in select cities. Hertz and Avis will add a total of 3,000 hybrid rentals to their fleets by the end of this year. For those who couldn't even find a Toyota Prius to test drive because the car sales have been so hot, this is also a chance to add an actual entertaining element to a vacation. Are the cars really as quiet as they say? Will I really get 50 mpg? Will Leonardo DiCaprio start returning my calls?, according to a story in the June 14 USA Today.