Under current procedures, the EPA certifies that new vehicles comply with emissions rules by signing off on test data submitted by automakers, which run the vehicles through the agency's prescribed testing cycle in their own labs. The EPA audits a small portion of new vehicles each year and has several other means to ensure compliance.
But despite those checks, and the penalties for automakers that flout the rules, VW was able to evade federal regulators for more than six years by installing software on some 482,000 diesel-powered vehicles that ran a different set of emissions controls when the vehicles were in test mode.
The EPA conducts so-called in-use tests on vehicles that already have been certified, but those tests are also done on the dynamometer and intended to ensure that emissions remain as clean after several years and many thousands of miles of driving as they are when vehicles roll off the assembly line.
"What VW was doing would not have been detected as part of in-use testing," said Margo Oge, former head of the EPA's Office of Transportation and Air Quality. "So the question in my mind is: Is the agency going to have to start thinking about how best they can prevent something like this from happening?"
On Sept. 25, the EPA informed automakers it would subject diesel vehicles to additional tests designed to detect so-called defeat devices like the software VW used. It purposely gave few details.
"We aren't going to tell them what these tests are. They don't need to know," Chris Grundler, the current director of the EPA's transportation office,said on a conference call that day.
"They only need to know we are going to be keeping their vehicles a little bit longer and driving them a little bit more."
The EPA may have been able to detect VW's excess real-world emissions by conducting on-road tests using portable emissions measuring systems. Grundler said the agency has 23 such testing units but has prioritized testing heavy-duty diesel engines, which account for the vast majority of nitrogen oxide emissions from diesels, and whose makers have been caught cheating in the past.
In that sense, self-certification presents a practical way for regulators to focus their finite resources on key priorities, even if it leaves them vulnerable to cheaters.
"It's very daunting to have a regime to control for this type of intentional cheating, which is very easy to do but also very hard to catch," said Roland Hwang, director of the energy and transportation program at the Natural Resources Defense Council. "It's always going to be a challenge to catch up to these guys when they cheat."
Effective changes instead would include "patching the holes in the current system, ensuring Congress adequately funds the EPA for enforcement and ensuring that the penalties are sufficient to deter future cheating," Hwang said.
"All these three things have to go together because it's simply not possible for EPA to test all 16 million new cars and go through every vehicle's 100 million lines of code."