One of the largest makers of consumer GPS devices has commissioned a study on fuel consumption in cars that have GPS devices and cars that lack the feature. The conclusion is that having a device that informs drivers about traffic can lower emissions. Of course, if you can avoid taking a car you should do so.

In a three pronged study which evaluated drivers without a navigation system, drivers with a navigation system, and drivers with a navigation system that included traffic, the results revealed that drivers using navigation devices 1) drove shorter distances and 2) spent less time driving. Conducted in two metropolitan areas of Germany – Dusseldorf and Munich – the study also showed that drivers with navigation devices had a 12% increase in fuel efficiency, as measured by liters of fuel consumed per 100 kms. Fuel consumption among those drivers using navigation fell from 8.3 to 7.3 l/100kms.
This increase in fuel economy translates to an estimated .91 tons (metric) decrease in carbon dioxide emissions every year per driver, or a 24% decrease over the amount that the average non-navigation user emits per year. Stated in terms of grams/km the reduction equates to 25 g/km per car. And with an annualized decrease in driving of nearly 2500 fewer kilometers per driver, 1.19 million tires would also be saved from disposal in Germany due to the decrease in wear and tear.