The Companion+ Mobile Safety app provides a fuel consumption index.
Although it is not directly connected to the vehicle, the app looks at your driving patterns to identify behaviors indicative of fuel waste, such as highway speeding or rapid acceleration on surface streets.
Factors such as these contribute more to fuel waste than commonly accepted beliefs about vehicle idling.
Fuel efficiency factors
Number of rapid accelerations
Time spent on speeds that exceed the globally established highway speeding limits of 65mph and 75mph, where air resistance becomes a major factor in increased fuel consumption.