Four days a year and 21 per cent less CO2 emissions. That’s what a GPS with real-time traffic information will give to you, and the entire planet. At least, that’s what maps maker Navteq says. As you can expect, there’s a catch.

The study—conducted in Dusseldorf and Munich, in Germany—had three groups: One with GPS without real-time traffic, another with GPS units with real-time traffic information, and a third one—the control group—without any GPS.

The results were clear, according to them: Drivers with real time-traffic information will spend 18 per cent less time going to places. That’s four days a year, which—if you ask me—is quite a lot. The study also found that these drives traveled shorter distances and times, which decreased yearly CO2 emissions an average of .79 metric tons. This resulted in 21 per cent less carbon dioxide.

So what’s the catch: Those percentages are compared to drivers “without navigation.” Their press release fail to provide information on GPS without real-time traffic information systems. Highly suspicious, if you ask me. [Autoblog]