How many miles a Chevrolet Volt can travel on a single gallon of gas is still up for debate. The EPA rejected the formula that General Motors used to calculate its 230 mpg estimate for the extended range vehicle. In GM's defense, it used a draft formula that the EPA developed for testing plug-in hybrid vehicles.
Using those calculations, GM has been promoting a 40-mile range on a single charge of the battery when driving the Volt in EV mode. Yet when using its gasoline-powered engine generator to propel the vehicle, the Volt would be able to extend its range to more than 300 miles, according to GM.
The EPA did not approve an alternate formula, but the Society of Automotive Engineers, which sets many standards used by the automotive industry, expects that the EPA will use the testing procedure that the group recently approved for evaluating plug-in vehicles and calculating their fuel economy. The SAE expects to publish that standard later this year. We hope that date will come soon, as the Volt is expected to be in production in November.
Source: USA Today