Illustration by Bloomberg View
Illustration by Bloomberg View

The U.S. automobile industry has come a long way since the 1970s. Today’s vehicles are safer, more fuel-efficient and more comfortable. Yet public policy toward cars is marred by standards set in 1978 that are as obsolete as a rusted Chevy Nova.

At issue is how federal regulators calculate each automaker’s Corporate Average Fuel Economy. Obscure as these CAFE ratings may be, their public policy impact is vast. Whenever the U.S. government tells automakers to boost their CAFE scores -- as it did this summer -- it transforms the next generation of cars Americans drive.

The trouble is, the tests used to gauge fuel efficiency don’t reflect the way we actually drive, especially on the highway. The government’s highway test involves a top speed of 60 mph, an average speed of 48.3 mph, no use of heaters or air conditioners and an achingly slow initial acceleration in which it takes more than a minute to go from zero to 50 mph.

It would be one thing if this exercise in pokey driving produced equally distorted scores for all models. But the outmoded CAFE process risks short-changing cars with smart fuel-saving features in favor of others that are engineered for the test.

An example: The Environmental Protection Agency’s CAFE test for city driving includes many momentary stops at stop signs, but only two or three longer stops of the sort made at traffic lights. This has the effect of devaluing stop-start technology, which switches off the engine when cars idle in traffic jams or at stoplights, and has proved popular in Europe and Asia.

Under current CAFE tests, says John Voelcker, the editor of Green Car Reports, stop-start technology would be scored far too low. It would seem to improve cars’ efficiency by barely 0.1 percent, even though one Japanese automaker thinks it could help big-city mileage as much as 5 percent.

For highway driving, tiny improvements in aerodynamics can make a big difference. Engineers can increase fuel efficiency by changing the slope of windshields, closing the front grille at high speeds and switching to slightly narrower tires. The payoff is modest at 50 mph; it is far greater at 70 mph, where air resistance is twice as intense. But with its 60 mph limit, the CAFE test fails to appreciate the gains.

The EPA has already devised sophisticated new ways to test how cars perform at high speeds, in cold weather and with air conditioning turned on. The EPA uses such data for showroom stickers, but pays it far less heed in the standard CAFE calculations. Under the current tests, the stated goal of 54.5 mpg by 2025 is a number that will be achieved only on paper, car experts say.

In practical terms, hitting the CAFE target is likely to produce a more modest 40 mpg to 42 mpg in real-life driving, analysts say.

Pushing for greater fuel efficiency is a good way to help the environment, save money for consumers and help reduce U.S. oil imports. If federal agencies could overhaul their metrics in the next year or two, we could get there faster.

To contact the Bloomberg View editorial board: view@bloomberg.net.