Like many drivers over the years, you may have wondered why vehicles (including hybrids) don't always seem to achieve the same fuel economy ratings estimated by the Environmental Protection Agency (EPA). The explanation is this: Until recently, these estimates were conducted under "ideal conditions" and not based on actual driving conditions, which may involve everything from operating the vehicle's air conditioning system to heavy stop-and-go traffic. With the 2008 model year, all of that changed.

The Environmental Protection Agency now calculates fuel economy estimates based on additional criteria designed to be more in line with "real-world" driving conditions. These include the city and highway tests used previously, along with additional calculations that take into account:

- Operating the vehicle at speeds in excess of 65 mph and faster acceleration
- Operating the air conditioner
- Colder outdoor temperatures

The result? The EPA's 2008 fuel economy ratings will generally be somewhat lower than in previous years. Yet, at the same time, they should more closely reflect the fuel economy that you can typically expect from your vehicle.