The United Nations Economic Commission for Europe (UNECE), which also covers Turkey, Israel, Russia, Canada and the United States, has the job of coordinating standards for fuel and energy consumption of vehicles. According to the protocol it has set for testing both pure electric and plug-in hybrid vehicles, energy consumption is to be measured when the vehicle is running solely on electric power at a constant speed of 50 kilometers per hour – that's a mere 31 miles per hour – without any acceleration or deceleration required. The electric range of the vehicle is then derived from the results. This figure is misleading because, aside from the obvious fact that real world driving requires acceleration and deceleration, the testing doesn't account in any way for wind resistance, which increases exponentially at higher speeds.
Here in the U.S., the EPA has no plans to use the UNECE's 31-mph consumption testing standard for electric and plug-in hybrid vehicles. Instead, it will use the same test cycle regular vehicles are subject to, but apply a snazzy new EPA sticker. Thankfully some automakers in Europe, like Volkswagen with its XL1 plug-in hybrid, aren't using this slow-speed testing procedure either, and instead choose to quote a more realistic consumption figure at double the speed (62 mph). The moral of the story here is before passing judgment on the range or electric consumption of an EV, make sure you understand what testing procedure was used to come up with the number.
[Source: Plugin Cars]