It was historic when President Obama announced a wide-ranging agreement with automakers and the state of California that will get cars to a whopping 54.5 mpg by 2025. Wow, 54.5 mpg! But did you know that, because of loopholes and outdated testing procedures (dating to the '70s) 54.5 mpg is really 40?

As ridiculous as it may seem, the current tests assume an Eisenhower-era driving experience, with steady 48-mph highway driving with no air conditioning, radio or even heater use. The Highway Fuel Economy Test was developed in 1974, and is conducted in a lab (at 75 degrees), by a professional driver using a dynamometer, with no accessories running. In the real world, we don’t drive that way — the radio blasts, the air is set at Arctic temperatures — and so the mileage we actually experience is much worse than the official numbers indicate.

Yes, so as far ahead as 2025, carmakers will be required only to deliver cars that achieve a measly real-world 40 mpg. The Sierra Club is sick and tired of this kind of thing, and just issued its Corporate Average Fuel Economy (CAFE): Truth Behind the Testing report that reveals the federal government’s dirty secrets.

According to Ann Mesnikoff, director of the Sierra Club’s green transportation program, actually improving the test protocols would require Congressional action. With deficit ceilings and more, this is just not on their radar screens.

To confuse matters even more, the tests that determine window sticker mileage are now much better than they used to be, having gone through a useful upgrade that includes a whole lot more environmental information (but not the letter grades that many greens had sought). It’s the separate tests for automaker compliance that are antiquated. “The whole system needs to be adjusted,” Mesnikoff told me. “The CAFE test results are still stuck in the 1970s, and give readings that are about 25 percent higher than the actual on-road numbers.”

My guess is that there won’t be test reform unless the public complains, and the facts about CAFE testing are so arcane that nobody even knows this issue exists. There's no squeaky wheel, and therefore no groundswell for change. But that, of course, is what the Sierra Club campaign is all about — getting people to pay attention.

According to Dan Becker, the safe climate campaigner for the Center for Auto Safety, “The Sierra Club report shows the deal reached by the automakers and the administration doesn’t go nearly as far on a gallon of gas as it seems.” According to Becker, Congress would need to write new legislation to make the test more accurate, because as written it can only be altered to become more favorable to automakers. “The inaccuracy is baked in,” he said.

But beyond bad testing, there’s much to like in the new rules. They should save $107 billion at the pump over their useful 2017-2025 life, says the progressive investor group CERES, and $8,000 per vehicle, says the EPA. We’ll save 12 billion barrels of oil (EPA) and create 484,000 jobs nationwide by 2030 (if we’d gone to 60 mpg, it would have been 700,000 jobs). Those last figures are from CERES, which also says that 43,000 of the jobs will be in the auto sector. There will be net job gains in 49 states, the group claims. In the CERES chart at right, use the 5 percent annual figure, because that's where the standards ended up. It's more jobs per gallon, the group says.

Don’t get me wrong, 54.5 mpg is good and a real achievement by the Obama administration. But it’s a rule that’s just not being all it could be. To help you understand what's at stake here, automakers will take a number of steps to get to 54.5 mpg, and they're detailed in this video:

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