The US Environmental Protection Agency ( EPA) may go back to the proverbial drawing board to figure out how to best test and rate plug-in hybrid-electric vehicles and extended-range plug-ins after certain Ford models were tested for less-than-advertised fuel economy, reports the USA Today.

The publication quoted Chris Grundler, the regulator's director of the office of transportation and air quality, saying that one major challenge is measuring all-electric driving range in a plug-in hybrid because such a range can swing wildly based on driving styles and other conditions. That means that vehicles like the Chevrolet Volt and Toyota Prius Plug-in Hybrid may receive adjustments to their testing methods going forward.

The EPA's reconsideration marks continued fallout from tests by Consumer Reports and groups like CleanMPG, which found Ford's Fusion and C-Max hybrids to get real-world fuel economy that was lower than the models' official mile-per-gallon EPA ratings.

Meanwhile, last month, Automotive News quoted a senior engineer at the EPA saying that the regulator may increase its number of audits to better guard against potential overstatements of fuel economy. That issue became all the more relevant after Hyundai and its Kia affiliate needed to reduce fuel-economy figures on a bunch of their models late last year, forcing the companies to set aside about $412 million for customer refunds stemming from the mileage overstatements.

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