Thanks to Dieselgate we’ve known since 2015 that vehicle emissions are higher in practice, and vehicle fuel efficiency is lower, than official tests show. Overseas studies have found that the gap is real and growing but how does that relate to New Zealand?
New research published by Emission Impossible Ltd and Mote Ltd for the New Zealand Transport Agency sheds new light on real-world emissions and fuel efficiency of New Zealand vehicles. The research developed a purpose-built portable emissions monitoring system (PEMS) in order to measure the real-world emissions of a representative cross-section of the New Zealand fleet (see Figure 1).
Figure 1. The PEMS equipment installed on one of the test vehicles.
Test vehicles were selected to represent the most common and influential sectors of the fleet, and included petrol and diesel, light and heavy-duty, New Zealand new and second-hand imported vehicles manufactured between 1996 and 2014. These were driven over a real-world route in Auckland, comprising city, open road and motorway driving with a range of vehicle speeds and gradients.
Real-world versus official standards
As with elsewhere in the world, our PEMS testing found that real-world emissions of most pollutants were higher than those allowed by the regulated standards.
Key findings were:
- real-world NOX emissions were generally higher than standards, with results approximately 4.6 times higher on average (ranging from two to nearly eight times the limit)
- real-world PM2.5 emissions for light-duty vehicles were similar to the standards
- real-world CO2 emissions were on average 17% higher than type-approved fuel consumption figures
- real-world NOX emissions for the tested vehicles were comparable to those for vehicles tested in Europe and Australia (see Figure 2).
Figure 2. Our PEMS results compared with Australian PEMS results for fuel consumption.
Sadly there was little evidence that mandatory reductions in emissions standards have had any impact on actual emission levels in reality. The only exception was PM2.5, for which emissions have reduced dramatically in later model diesel vehicles, we think due to the increasing effectiveness of the particulate filters used.
Unfortunately there was also little evidence that fuel consumption has improved over time – CO2 levels typically remained stubbornly in the 200 g/km to 300 g/km range, irrespective of the type of vehicle or fuel used.
Still. Now we know. Right?
To read more:
Testing New Zealand vehicles to measure real world fuel use and exhaust emissions, NZ Transport Agency research report 658, available online at www.nzta.govt.nz/resources/research/reports/658