So many records

used in the Colorado cleanair program, also found that the VW diesel engines spewed a much higher ratio of nitrogen dioxide, which Bishop said is much more toxic.

About 60 percent of the NOx emissions from the VWs consisted of nitrogen dioxide, compared with 10 to 30 percent before 2009.

McClintock and Bishop said they didn’t connect the dots to conclude VW had manipulated its emissionscontrol software. That would have required the ability to reverse- engineer a proprietary system.

Credit for uncovering the cheat has mostly gone to the University ofWest VirginiaCenter forAlternative Fuels, Engines and Emissions, which placed portable emissions monitors on a 2012 VW Jetta, a 2013 VW Passat and a BMWX5 SUV.

Colorado’s remote emissions testing system is the nation’s most comprehensive, capturing about 7 million readings a year on nearly every kind of vehicle running in theU. S., McClintock said.

Testing stations use remote sensors and cameras that snap a shot of license plates, which can be linked to a vehicle identification number, or VIN. The VIN contains detailed information on a vehicle’s year, make, model, engine and fuel type.

Colorado’s remote sensors did capture the higher VWand Audi emissions, as McClintock’s research found, which raises the question of whether the state could have sounded an early warning.

But nobody at the state wasmining the vast trove of remote data for that purpose — nor were they required to.

The RapidScreen program’s emphasis, as dictated by the legislature, is on “clean screen” or finding cars that can skip emissions testing, rather than calling out polluters.

RapidScreen tests also aren’t reviewed for diesel engines, which in Colorado fall under a more limited emissions testing program than gasoline engines, said Christopher Dann, a spokesman for the state’s Air Pollution Control Division.

“The diesel inspection in Colorado is visible smoke,” Dann said. “Opacity is the way to identify broken diesel vehicles.”

That means Colorado looks for soot or particulates but doesn’t measure for NOx and other emissions, as it does in gasoline engines.

And even if the statemeasured more components in diesel engine emissions, it probably still would have missed the VW problem. New diesel vehicles are exempt from testing for four years, and the manipulation uncovered appears to have started in 2009.

“We aren’t designed to anticipate a major vehicle manufacturer cheating to defeat the system,” Dann said.

Dann said diesel cars, such as theVWsedans and station wagons, represent about 11,000 of the5million vehicles on Colorado roads.

Bishop and McClintock said they don’t know preciselywhat role the Colorado testing data played in federal regulators taking the actions they did.

One possible scenario is that VW was presented with evidence from multiple sources until it cracked, Bishop said. If so, Colorado drivers unwittingly helped break the case.

VW said it would set aside $ 7 billion to cover the costs of correcting the problem and restoring consumer confidence.

McClintock said he would like to see some of the fines go toward expanding the use of remote emissions sensing equipment beyond the six states that currently deploy it.