When a user goes to the site and selects the car or truck they have and the annual miles they drive the calculator displays the current mileage and what could be achieved with current technology. It then displays how much money you would save. The problem is that much of the data in the calculator is incorrect. For example selecting the Ford Escape hybrid shows a current mileage of 33mpg and a potential of 62mpg which seems highly unlikely. Choosing the Prius or Civic hybrid brings a response that the vehicle is already achieving maximum fuel economy. If an Escape Hybrid could almost double it's mileage why not these two?
If you select a Toyota Yaris it reports the current mileage as 22.7 mpg and potential of 39.7mpg. I suspect most Yaris drivers would be very surprised and suspect something is wrong if they got mileage that low. The same result comes up if you select a Honda Fit or numerous other cars. According to the site the current numbers are based on EPA ratings but clearly they have entered a lot of erroneous data. The idea is a good one, but if the results are so wrong it can be counterproductive and damaging to the club's credibility. They should really take the calculator off line until they correct the errors.
Update: Someone from the Sierra Club posted in the comments that they are aware of some errors and are updating their database.
[Source: Sierra Club via Green Options]