The importance of fuel economy is simple - it saves you money. The way that you drive and maintain your car can also affect its fuel economy.
If a driver who travels 15,000 miles (24,000 km) a year switches from a vehicle with 10 mpg to 12 mpg average fuel economy (0.10 gallons per mile to 0.083 gallons per mile), 250 gallons are saved. A similar 20% improvement in exchanging a 30 mpg for a 36 mpg (0.033 gallons per mile for 0.027) vehicle saves only 83 gallons. Because mpg and fuel consumption are inversely related, both can be misinterpreted.[6]
For example, 20% lower l/100 km does not mean 20%, but 25% more distance. This comes from the following calculation: 20% is 0.8 times less fuel, therefore 100% / 0.8 = 125% of the original distance, or 25% further on every litre. Changing from 14 to 20 MPG saves twice as much fuel over a given distance as the improvement from 33 to 50 MPG[7]).
A measure of gallons per mile (GPM), such as gallons per 100 miles, provides a one-for-one comparison of the consumption for a given distance of driving. Unlike MPG, the GPM of one car can be subtracted from the GPM of another car to get a direct measure of fuel savings. Inversely this becomes a moot point to the driver who wishes to get the most traveling out of a tank of fuel. Here the MPG values give a clear measure of "bang for your buck" and are directly comparable; an improvement of 20% MPG means 20% more traveling for any car. In this case comparing the difference in GPM values would be misleading. (e.g. an improvement from 0.2 to 0.1 GPM gets the driver twice as far on a tank, but an improvement of 0.3 to 0.2 GPM only gets the driver 50% further.) Since many people do not know how far they will drive, but know how large their fuel tank is, the MPG value remains more useful to them.
Why fuel economy is important
The importance of fuel economy is simple - it saves you money.
A fuel efficient car makes personal sense. The less fuel you use, the more money you save. The way that you drive and maintain your car can also affect its fuel economy.
At the moment, most vehicles run on either petrol or diesel (fuel that is also known as 'fossil' fuel). There isn't an endless supply of 'fossil' fuels and this is a problem given the high energy use of the transport sector: transport makes up 44% of national energy consumption. Of this, passenger transport makes up 57%.
To tackle this problem:
alternative fuels are being researched
biofuels (alternative fuels produced from renewable resources) are becoming available at the fuel pump. (Check with the manufacturer to see whether your car is compatible.)
technology is being developed to make engines more efficient
more 'hybrid' and electric cars are becoming available. Hybrid cars can switch between electric battery power and fossil fuels, whereas electric cars run solely on electric battery power.
There's also a new interest in small diesel-powered and hybrid cars.
