The ongoing Volkswagen diesel-emissions scandal has, to say the least, exposed weaknesses in the U.S. Environmental Protection Agency (EPA) testing regime.
VW was able to get away with installing "cheat" software on 482,000 cars from model years 2009 to 2015.
But it wasn't until independent researchers tested one of these cars that the deception was discovered.
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Still, it appears that it could have been worse. While U.S. emission tests are based on very gentle, 40-year-old driving cycles, the emission limits carmakers must meet are tougher.
European emissions-testing standards not only offer greater opportunities for cheating, they're also worse at predicting real-world emissions and fuel efficiency, according to the Economist (registration may be required).
The European Union is less stringent about nitrogen-oxide (NOx) emissions than the U.S., instead focusing more on fuel economy and carbon-dioxide emissions.
2014 Volkswagen Jetta SportWagen
While standards for those factors in Europe are reportedly very tough, they don't bear much resemblance to what cars return in real-world use.
The difference between rated fuel economy and what drivers are actually seeing has grown to 40 percent in recent years, says green advocacy group Transport & Environment.
Indeed, European fuel-economy ratings tend to be much more optimistic than U.S. EPA ratings.
ALSO SEE: European Makers: NOx Limits Must Rise For Real-World Emissions Tests
In part, that's because the EPA applies numerous "adjustment factors" to the raw emission-test data to create window-sticker fuel-economy ratings that roughly resemble reality.
Further, there are reportedly even greater opportunities for cheating in Europe than the U.S.
In the U.S., carmakers test their own cars and then submit the results to the EPA, which also audits results by testing a handful of cars itself each year.
2014 Volkswagen Jetta SportWagen
In Europe, testing is contracted out to private firms, which compete for carmakers' business.
That appears to create an incentive to doctor test results to keep clients happy--including modifying test cars.
Items such as sound systems are removed to lower weight, mirrors are removed, and gaps between body panels taped to reduce drag, reports the Economist.
MORE: Will European Fuel-Efficiency Tests Get More Realistic Under New Rules? (Jul 2014)
Tires can also reportedly be over-inflated, alternators disconnected, and cars run only in very high gears.
While its resources are limited by budgetary concerns, the EPA can conduct tests of its own to catch cheating like this--and levy fines.
In 2014, it fined Hyundai and Kia a total of $300 million for misstating fuel economy; Ford subsequently restated mileage figures for six of its cars. This generally does not happen in Europe.
2016 Volkswagen Beetle TDI Convertible
Volkswagen's cheating in the U.S. was the result of a pattern of behavior the "European system created," said David Kodjak of the International Council on Clean Transportation, the organization largely responsible for uncovering the carmaker's cheating.
Europe is considering stricter testing standards, which could be enacted as early as 2017.
In response to the VW scandal, PSA Peugeot Citroën also says that it will begin publishing real-world fuel-economy test results, according to Automotive News Europe.
The information will be compiled by an independent body, and should be available next spring, the carmaker says.