Volkswagen's diesel-emissions cheating went on for more than six years in part because the company's use of "defeat device" software was hard to detect.
It wasn't until researchers from West Virginia University and the International Council on Clean Transportation (ICCT) decided to confirm laboratory results with on-road emissions testing that the deception was uncovered.
On-road testing isn't currently required to certify new cars for sale in the U.S., although that may change in the wake of the VW scandal.
If that's the case, expect to see more cars sporting contraptions like the one in the video above.
That knot of wires, tubes, and other hardware is a Portable Emissions Measurement System (PEMS)--the same piece of equipment used to detect the Volkswagen "defeat device."
It's essentially a scaled-down version of laboratory emissions-testing equipment, as California Air Resources Board (CARB) air-pollution specialist John Swanton explained to Lou Ann Hammons of Driving the Nation.
Portable Emissions Measurement System (PEMS) (Photo by Millbrook Proving Ground)
Hoses attached to the tailpipe collect exhaust gases for analysis, an array of electronics is strapped down in the back seat, and a generator mounted off the rear bumper provides power for all of it.
Normally, emissions tests are conducted on a dynamometer or "rolling road," with the car stationary and conditions tightly controlled.
Volkswagen's decision to use "defeat device" software was based on the assumption that regulators would never try to verify laboratory results with on-road testing.
The software was designed to detect the specific conditions of those laboratory tests and temporarily alter the way the diesel engine functioned, to make the given car comply with the relevant emissions standards.
But when ICCT researchers studied European diesel cars, they noticed on-road emissions of some models were significantly higher than the results from lab tests.
They decided to test cars in the U.S. as well, first testing the vehicles to a dynamometer, then strapping on the portable test equipment to measure their real-world emissions on a road trip from San Diego to Seattle.
2009 Volkswagen Jetta TDI
They found that two separate Volkswagen models were way over U.S. emissions limits.
A Jetta TDI emitted as much as 35 times the legally-allowed levels of nitrogen oxides at certain points during the test.
That a third party discovered Volkswagen's cheating is likely the most persuasive argument yet for on-road emissions testing.
MORE: EPA Will Test New-Car Emissions On The Road After VW Scandal (Sep 2015)
This was discussed after recent fuel-efficiency rating reductions by Hyundai and Kia, as well as Ford.
Like CARB, the U.S. Environmental Protection Agency has the PEMS equipment needed to conduct on-road testing, but its limited resources mean that option is rarely exercised.
Legislation is now pending in the European Union to add real-world testing to certification procedures, but as yet, the EPA hasn't made similar moves.