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ICCT: US 2010 compliant trucks emit more NOx in real driving than Euro VI vehicles

4 May 2020

There is a significant gap between real-world and certified NOx emissions from heavy-duty diesel vehicles. This gap is especially wide during urban driving conditions and other low-load operations in diesel HDVs certified under the US EPA 2010 program, finds a new report by the ICCT.

The ICCT report compares NOx emission values from 11 HDVs designed to meet the US EPA 2010 NOx standard with five European trucks designed to meet the Euro VI NOx standard. The analysis finds that European HDVs are better designed than US trucks to control NOx emissions under low-speed, low-load, and idle conditions. The US HDVs studied emitted on average 1.4 times more NOx per unit work than the European vehicles. During urban driving conditions, work-specific NOx emissions of US HDVs almost quadrupled in magnitude compared to their total route emissions. For European HDVs urban driving emissions were twice as much as their total route emission values. US trucks emitted more NOx than the European trucks at the lowest power range, including idle. Below 10% of maximum rated power, the sample of US trucks emitted twice as much NOx as the sample of European trucks studied.

NOx emissions by speed bin for European and US HDVs. Error bars show confidence intervals at 95%.

The report also analyzed the tools used for analyzing PEMS data and determining in-use emissions compliance—the US Not-to-Exceed (NTE) and the European moving average window (MAW) protocols. The analysis of the in-use compliance tools indicates that excluding data from the regulatory evaluation directly impacts in-use NOx emission values, concluded the ICCT. The US NTE protocol evaluates in-use NOx data only under a narrow band of vehicle operating conditions, exclusively during highway driving. In contrast, the European MAW method for in-use compliance evaluation better captures NOx emissions at low-speed and low-power demands that are characteristic of urban driving.

The data for the NOx emissions comparison came from PEMS tests carried out in US and EU trucks by several testing institutions. The 16 vehicles that were selected included 11 US Class 8 vehicles (MY 2010-2015) certified to meet the EPA 2010 0.2 g/bhp-hr NOx standard, and 5 EU N3 vehicles (MY 2012-2016) certified to Euro VI standards. Engine displacements for the EU and US trucks were, on average, 12.4 L and 12.8 L, respectively. Manufacturer names were not disclosed because some data sources required vehicle and engine anonymization.

Source: The ICCT