Talk about the hybrid car scam! With the exception of the Prius, it seems like most hybrids have highway mileage somewhere in the 30--35 mpg range. This is a little better than those same car models with a gas engine. But I own a 1984 Honda hatchback, obviously not a hybrid, which gets 40-odd mpg on the highway, and I remember it being pretty routine in the 1980s and 1990s for economy cars or even 4 door models to have comparable mileage. I imagine it mostly has to do with the massive increase in horsepower in recent years, or maybe heavier cars as a result of safety features. But how are hybrids supposed to help us out of the global warming/foreign oil dependence trap when they are less efficient than a 24 year old non-hybrid beater? And why not just make cars like the aforesaid beater, with a hybrid engine in them?
Over time, technology improves, and we develop more efficient ways of burning gasoline as a way of making a car move forward. Those kind of advances can be used to reduce the overall quantity of gasoline burned, but they can also be used to increase the overall power of engines. That's the basic problem being pointed to here, and it's why if you want to reduce carbon emissions there's ultimately no substitute for an emissions cap or a carbon tax. If you create a financial incentive to reduce emissions, then our vast ingenuity and entrepreneurial spirit will produce vehicles that accomplish that goal. If we don't, it won't, as even the very same technologies that could reduce gasoline consumption are instead turned to other purposes.
Meanwhile, it's important to remember that for the short-tun the most important thing isn't to develop futuristic new low-emissions vehicles. The low hanging fruit is to replace the very least efficient vehicles with more efficient ones. Replacing an SUV with a standard sedan does more to cut consumption than does replacing a sedan with a hybrid. Even replacing an SUV with a minivan brings about substantial reductions.