It was 1998. The EPA had just settled the largest Clean Air Act enforcement action in its history, for one billion dollars, with seven manufacturers of heavy-duty diesel engines who were found to have cheated the emissions regulation. The manufacturers had used software defeat devices that allowed an engine to pass certification tests in the laboratory but then run in more polluting but more fuel efficient ways during highway driving. As part of the settlement, the manufacturers agreed to additional engine emissions testing, both in the lab and on the road, in order to prove compliance.
Buried in Appendix C of the Consent Decree between the federal government and Caterpillar, Cummins, Detroit Diesel, Volvo, Mack Trucks/Renault and Navistar was a definition of the test that would be used for that additional compliance testing: the Not to Exceed (NTE) test. In 2005 the NTE was incorporated into the EPA’s “Final Rule for Control of Emissions of Air Pollution From New Motor Vehicles: In-Use Testing for Heavy-Duty Diesel Engines and Vehicles,” the first regulation in the world to mandate in-use testing of heavy-duty vehicles. And U.S. federal heavy-duty vehicle emissions regulation still relies on the NTE today, and will continue to do so until at least 2027.
It bears repeating: the test used to monitor and certify emissions performance of heavy-duty engines in the United States was devised somewhat hastily, under the pressure of negotiating a settlement to a legal case involving a specific type of cheating during highway operation in which a billion dollars was at stake (real money in 1998). It’s no wonder that it doesn’t work the way it might have if it had had a different starting point.
What is the NTE test? A technical description can be found here, but in brief, the NTE test places limits on exhaust emissions during real-world highway-type driving. The NTE test does not place any limits on emissions during other kinds of driving, such as low-speed or low-load operation, urban operation, or transient driving (lots of different speeds and accelerations and decelerations). And because U.S. regulations rely so heavily on the NTE test, they don’t effectively address emissions in those conditions. Unsurprisingly, heavy-duty vehicles on the road in the United States today have very low emissions during highway driving and very high emissions during urban driving. In fact, as diesel trucks exit a freeway to enter into a heavily populated area, the harmful emissions in their engine exhaust increase by an order of magnitude.
Please click here to view the full press release.
SOURCE: ICCT
