The simple truth is Manual Transmission vehical's get better milage than automatics. EPA estimats to show this is true.
A 2008 Honda Civic
Automatic: City - 21, Highway - 31
Manual: City - 22, Highway - 31
A small gain but there. These are probly not the best examples of the diffrance and as with all things the diffrence will varry with car and driving habits ,but the manual transmision will give better gas milage and performance for the life of the vehicle This is because a automatic transmision has losses such as the torque convirter that a manual transmison does not. A manual transmision can be 5%-10% more fuel efficient (the Epa's testing does not acount for driver habits). It also responds better to changes in driving habits since the driver is in more control and not a computer controled transmision(as with most automatics) made to please everyone from the wanabe racer to a fuel milage minded driver or the grandma that cares about nothing but the smoothest possiable shifts meaning no one is perfectly happy , but with a manual the driver controls the charcterists of the car. The maunal transmision is normaly cheaper to buy and has and incredibly long life (1979 ford 150 350,000 miles no transmision work, ford tarus sho 230,000 miles no transmision work ,both still running) vs. and automatic (1992 Pontiac Transport Minivan, transmision failure at 180,000 miles). Manual transmisions also weigh less than automatics and less weight means more fuel milage and better performance.You can save money and the environment while having more fun driving. Who said green means slow and boring? Do yourself and the world a favor buy a car with a manual transmision. Its just going to be harder to multi-task so stop that to become a safer driver. The link below reinforces the above text.
2008 Ford Mustang with the v6 engine
Automatic: City - 16, Highway - 24
Manual: City - 17, Highway - 26
The v8 only gains one mile per gallon with the manual on the highway but that is still a gain.
If all cars in the United States had manual transmisions then we would use about 38 million gallons a day less then we do now. That is 760 million pounds of CO2 It is a rough estimate and does not acount for manual cars on the road but does hint at the potintial. At the adverave number of miles an American drives, 16,500 miles at 25 Miles per gallon in an automatic would use 660 gallons of gas and produce 13200 pounds of CO2. While the same car with a 10% effincy boost would get about 27.5 Mpg, use 600 gallons of gas and produce 12000 pounds of CO2, saving 60 gallons of fuel and 1200 pounds of CO2 just from shifting your own gears and at $2 a gallon save you $120.
The savings below does not reflect the innital savings of buying the manual transmision car.reference link: http://centsprout.wordpress.com/2007/12/05/fuel-efficiency-with-a-manu