In-lab or on-road: Best new diesel-vehicle emissions-testing protocol?

On-the-road under real-world driving conditions or in the laboratory under non-real-world driving conditions, which is the best method for measuring emissions from new diesel vehicle exhaust systems? – that is the question. Auto manufacturers may tend to favor in-lab testing programs while all people who are affected by vehicle emissions in a health context might argue that on-road or in-transit emissions testing of new diesel vehicles produces the more relevant of results. In reality, though, is it six-of-one, half-a-dozen of the other or either way is okay, in other words?

Two Cycle Diesel engine with Roots blower
Two Cycle Diesel engine with Roots blower

What this has to do with is the prevalence of NOx (nitrogen oxides) and other harmful pollutants coming from diesel motor vehicles and in particular across Europe. Upwards of 500,000 Europeans are dying prematurely from said and other pollutants from diesel engines and other sources annually.1 It was revealed in a new Transport & Environment (T&E) report, that nine out of 10 new diesel automobiles tested by T&E produced NOx emissions under real-world driving conditions of as much as 22 times above accepted limits. 2 In fact, testing performed by this independent group found that diesel vehicle models were emitting into the air NOx emissions anywhere from seven to 22 times the acceptable health threshold for this harmful pollutant. Put alternatively, that’s unacceptable.

In support of this in “Clean diesels: Are they or aren’t they … ‘clean’?” it is written: “The International Council on Clean Transportation (ICCT) press release: ‘New ICCT study shows real-world exhaust emissions from modern diesel cars seven times higher than EU, US regulatory limits,’ of Oct. 11, 2014 is quite telling.

“The ICCT declared in no uncertain terms, ‘On-road nitrogen oxides emission levels of modern diesel cars are on average about seven times higher than the limit set by the Euro 6 emission standard, which went into effect September 2014. This is the key finding from a new report published today in Berlin by the International Council on Clean Transportation (ICCT), an independent research organization.’

“‘The study, which is the most comprehensive report on the real-world behavior on the latest generation of diesel cars published to date, found remarkable differences among individual vehicle models, indicating that technologies for real-world clean diesels already exist but are not being employed consistently by different vehicle manufacturers,’ the ICCT went on to state. ‘The findings come at a time when the European Commission is preparing to propose an improved car emissions testing procedure, including on-road measurement, that could take effect in 2017.’”

“According to the research organization, in the EU, around half of new cars, are diesel-powered.

“Added the ICCT: ‘The European Commission is currently preparing to require on-road testing as part of the passenger car type-approval process in the EU. According to these plans, vehicle manufacturers from 2017 would have to test new vehicles not only under laboratory conditions but also on the road, using PEMS [Portable Emissions Measurement Systems] equipment.’”

There is nothing vague about any of the above in the least.

Furthermore, it isn’t that in-lab testing is a non-valid method of emissions evaluation. This has been the established means of testing. But random testing may just produce results that could prove to be more reliable, meaningful. And, shouldn’t the goal or mission be to get the more or most reliable, valid results of the two methods of testing, anyway? Random testing of new diesel light-duty vehicles would make it virtually impossible that a doctored vehicle (one that performs optimally under test) would be selected as a test candidate.

The long and short of this whole new-diesel-vehicle-testing issue is not to dissuade motorists from buying/driving diesel-powered vehicles, but if these vehicles are to have a place on European roadways, then they should at least meet emissions standards and on-road testing might just be what the doctor ordered in order for such to be achieved.

For more on this issue, see: “Just one in 10 new diesel cars is clean as the legal limit, report finds,” press release, Sept. 14, 2015, from Transport & Environment and “Vehicle emissions testing in the EU: Why we are still struggling with the dead hand of the past—and what the future is likely to bring,” Sept. 9, 2015 blogpost from The International Council on Clean Transportation (ICCT).


  1. Transport & Environment, “Don’t Breathe Here: Tackling air pollution from vehicles,” Sept. 10, 2015,
  2. “Nine out of 10 new diesel cars exceed EU pollution limits, report finds: Road test reveals cars emit seven times the permitted level of exhaust emissions in real-world conditions,” by Damian Carrington, The Guardian, US edition, Sept. 14, 2015,

Image above: Pearson Scott Foresman

About Alan Kandel

Alan turned hardscrabble technology related experience into a professional writing gig and has never looked back. Alan resides in California's heartland - the San Joaquin Valley.

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