EPA Refines Guidelines for Fuel-Economy Testing, Promises Stricter Enforcement

Ford Focus MonroneyEarly last year, Environmental Protection Agency compliance director Byron Bunker made it clear to carmakers that procedures related to fuel-efficiency tests would be strictly enforced. He specifically addressed the coastdown tests used to determine settings for the chassis dynamometers the EPA uses to check emissions compliance, and to measure city and highway fuel economy. Now we know more about this.

In 2011, manufacturers began supplying vehicles to the EPA so the agency could verify the accuracy of the coastdown test results the companies had submitted. These tests are conducted on a level straightaway during low-wind conditions to assess a vehicle’s road load, which is comprised of aerodynamic drag, tire rolling resistance, and driveline friction. The results are used to program the indoor chassis dynamometers at the EPA lab to closely replicate “real-world” conditions.

Past abuses of EPA procedures involved at least one automaker disabling the brakes at three wheels in order to reduce friction—giving the test cars only one operational brake—and extended engine idling prior to the start of coastdown testing to warm all the underhood driveline bearings and joints.

Starting with the 2017 model year, manufacturers must provide detailed descriptions of their testing methods to the EPA, defining exactly how they determined their road-load dynamometer settings. The EPA also has clarified the minimum allowable number of miles accumulated by the tires and specifications regarding the surface texture and composition of the test track.





Manufacturers dinged in recent years by the government for selling cars with inflated fuel-economy ratings include Ford, Hyundai and Kia, and Mitsubishi. The EPA began spot-checking manufacturers’ submissions in 2011 by conducting its own coastdown tests on roughly 10 percent of new vehicles, a small number limited by the EPA’s staffing and resource levels. Now in the event a discrepancy in road-load energy loss is discovered that exceeds 10 percent in city driving or 7 percent in highway driving, it will result in the correction of the mpg figures on a given vehicle’s window sticker. EPA spot checks have increased to 20 percent of the new-car fleet in recent years, and it’s highly likely that even more cars will be checked for the 2017 model year.

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