So this story today about the new GM Volt to come out that supposedly gets 230 mpg. My first thought when reading it is that they are touting it as fossil fuel saver, and I'm skeptical. Essentially you are replacing one fossil fuel with another (whatever the electric company uses versus gasoline). There is no guarantee that the electric company will use less fossil fuel than you would use, say, per mile of driving. And there is no guarantee that the electric company will use *cleaner* fuel than gasoline. Plus, batteries tend to be notoriously difficult to dispose of, and are an environmental hazard themselves when thrown out.
One advantage to replacing mobile power (e.g. gasoline) with stationary power (e.g. electric company) is that one can replace the stationary power with nuclear, which you just can't do with cars.
It is claimed that it will be cheaper for end users, "In Detroit, where off-peak electricity rates are 5 cents a kilowatt hours, it will cost about 40 cents to recharge batteries overnight." One does have to factor in the maintenance costs, battery replacement, and battery disposal costs into the cost of owning this new car.
Now, I am not against this development, as such, but it is important (as always) to be aware of both the benefits and the costs of the new technology. It is far too easy to read one side of the equation, pat oneself on the back, while ignoring the hidden costs.