A study of 111 hybrid drivers found that the average fuel economy for 47 drivers of 2004/2005 Priuses was 49.95 mpg, or 9.2 percent less than EPA's combined estimates, Hybridcars.com reports. Hybridcars.com conducted the study with Claudette Juska and Charles Griffith of the Ecology Center of Ann Arbor, Mich., and auto economist Walter McManus. The testers recruited over 300 hybrid drivers eight months ago but narrowed the test sample size to 111 drivers to root out inaccurate results. In addition to the Prius results, the testers found: · The average fuel economy of 34 Civic Hybrid drivers was 47.36 mpg, or 0.8 percent more than EPA's combined estimates.
· The average fuel economy of 7 Accord Hybrid drivers was 31.81mpg, or 0.6 percent less than EPA's combined estimates.
· The average fuel economy of 5 Escape Hybrid (4wd) drivers was 28.57 mpg, or 7.8% less than EPA's combined average.
· The average fuel economy of 5 Lexus RX400h drivers was 25.15, or 13.3 percent less than EPA combined average.

They also concluded that:
· Using the AC or heat could decrease the ratio of actual to expected fuel economy by nearly 3.5 percent.
· Driving on hilly terrain could increase the ratio by 3.2 percent or more.
· Adding 10,000 miles to the odometer could increase the ratio by 3.0 percent, suggesting a learning curve for hybrid drivers.
The Web site states, “…the large and unavoidable variability in driving behaviors and driving conditions presents a huge challenge in determining actual fuel economy figures.”
The Web site plans to offer mileage tracking soon, which will allow users to create a hybrid blog, upload photos, track mileage and interact with other hybrid drivers.