Issue: Jan 2007


by Bob Brooks

Largely overlooked by press reports on the EPA’s new MPG label information to appear on 2008 and later US models is a shift in emphasis on the degree to which vehicle fuel economy is influenced by driver behavior.

For vehicle model years 1984 through 2007, the city and highway mpg data averages appearing on labels are adjusted to 10% less than the mild FTP (federal test procedure) for city driving and 22% less than the FTP highway mpg test numbers.

Based on discussions with Dennis Rakicki, Daimler Chrysler regulatory affairs engineer
and his counterpart, Tom Stricker at Toyota, starting with 2008 models the current adjusted data will be further adjusted down on average by 12% for city driving and 8% for highway driving... The engineers explain this reflects more comprehensive recent 5 cycle composite testing to reflect the original FTP city and highway conditions but also cold temperatures, aggressive driving and use of air conditioning. The FTP test data applied to car maker corporate average fuel economy requirements will not change.

The new label (EPA proposed sample attached) starting with 2008 models will indicate, for example “Highway MPG 25” immediately under which and readily noticed is “Expected range for most drivers 21 to 29 MPG”. This compares with labels for 2007 back through 1984 models which displayed the disclaimer under “Actual Mileage” off to one side followed in fine print with the wording “Will vary with options, driving conditions, driving habits and vehicle condition. Results reported to EPA indicate that the majority of vehicles with these estimates will achieve (followed by city and highway numerical ranges in equally fine print)” The “Actual Mileage” disclaimer is retained but separated from the new display of “Expected range” data.

Unknown is the percentage of motorists who experience mpg values outside the so-called
“Most drivers” category. Also, Richard Brean, an experienced car dealer salesman at Classic Chevrolet, Waukegan, IL tells AI that the new numbers in his view will mean “next to nothing” to most car buyers unless auto makers, the automotive media, EPA and other interested groups make an effort to explain the influence of driver differences separate from other factors...

Toyota engineer, Stricker, adds that the Prius hybrid car’s combined new mpg for 2008 will be 16% reduced from 2007 rather than 10% reduction for the average conventional midsize car. He says this reflects calculations based on the 5 cycle composite numbers but he stresses that on the basis of fuel used per unit of miles vs. miles traveled per unit of fuel, the hybrid’s fuel efficiency is good. Toyota executive engineer, Dave Hermance, recently killed in an aerobatic aircraft accident, was a strong advocate for the fuel use per unit of distance system (liters/100km) used in Europe and elsewhere.

Adding to the emerging debate about vehicle energy efficiency are reported efforts by US auto makers to replace the current corporate average fuel economy (CAFÉ) rule with a system that would set fuel economy standards for vehicles in different size/weight groups. This would favor makers with major positions in the larger vehicle group by reducing their need to produce smaller cars as fuel economy offsets. Adding to the complication will be the special mpg credits given to vehicle makers for flex-fuel vehicles that seldom if ever use high alcohol content fuel such as E-85 which cuts vehicle mpg by a third. Also difficult to judge will be the basis for claimed percentage gains from new technologies such as direct gasoline injection, cam phasing, compression ratio increases and new transmission systems.

About the author: Bob Brooks is a member of the Society of Automotive Engineers and long time automotive technology journalist specializing in powertrains and fuels.

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