I'll use some rough numbers to illustrate. You trade in your Civic, which averages about 32 miles per gallon, and buy a Prius, which gets a whopping 47 mpg. You've bumped up by 15 miles per gallon -- a big deal, right?Sort of.
Over the next 15,000 miles of driving, you'll have reduced your fuel consumption by 150 gallons. That's fine. But consider what happens when you upgrade your SUV. That's where the real action is.
You swap out your Dodge Durango (16 mpg on average) for a Toyota Tacoma (23 mpg). It's an upgrade of just 7 miles per gallon. It seems tiny. But consider that over the next 15,000 miles, you will have saved 285 gallons of fuel -- nearly double what your fuel-sipping neighbor saved.
Now change the numbers so that the car swap goes from 50 MPG to 100 MPG and the SUV swap goes from 15 MPG to 18 MPG. Let's also change the miles driven to 18,000 so we don't get any fractions. Over the course of 18,000 miles, the 100 MPG car uses 180 gallons of fuel while the 50 MPG car uses 360 gallons of fuel. That's a reduction of 180 gallons. Now for the SUVs. The 18 MPG SUV uses approximately 1000 gallons, while the 15 MPG SUV uses 1200 gallons. The SUV driver cuts his fuel usage by 200 gallons, or 20 more gallons than the car driver.
Therefore, the 100 MPG breakthrough is less important than getting a few more MPGs out of our trucks and SUVs.
