Nissan and the Japanese city of Yokohama plan to offer an iPhone application that's intended to encourage local residents to drive more efficiently, hoping to help them save gas and go easy on the environment.

Developed by Nissan, the iPhone eco-driving application links to the car over a Wi-Fi connection and monitors the acceleration, cruising speed and deceleration of the vehicle. The data is then uploaded to a central server, where it's compared to optimal driving profiles to rate the user's driving in these three areas on a scale from one to five. The application also gives the user an overall score that rates how environmentally friendly their driving is.

Because the eco-driving application monitors the car's speed, it's just an approximate measure of fuel consumption, said Stephane Bouet, of the Nissan Research Center, who developed the application. But the data is still good enough to give users a general idea of how their driving stacks up, he said.

Nissan demonstrated the eco-driving application at the Ceatec exhibition in Japan, offering visitors to the show the chance to drive a Nissan car around nearby streets and rate how environmentally friendly their driving habits are.

The eco-driving application will be used in a trial conducted with Yokohama to encourage more economical driving habits, but it's not yet clear if the application will be made widely available, Bouet said.