Cleaning up the diesel vehicles already on the road

Older diesel vehicles are prime culprits when it comes to both urban air pollution and climate change. Although they usually make up only a small percentage of all the vehicles in a region, they could account for half of total particulate matter (PM) and NOx emissions. Diesel exhaust is deeply concerning for two reasons. First, it contributes to a host of human health problems, including cancer. Second, diesel PM, also known as soot, is made up mostly of black carbon, a potent climate pollutant. Black carbon is now thought to be the second highest contributor to global climate change after CO2.

Stringent emissions standards (like those described in our model regulatory program, for example) can reduce emissions from new diesel vehicles to near-zero levels, and they are critical to any long-term emissions reduction strategy. But the impacts of new vehicle standards are only realized as the fleet turns over and the population of cleaner vehicles slowly increases. For classes of vehicles with relatively long useful lifespans (especially diesel trucks), it can be years before the benefits of such policies are felt.

Of course, comprehensive vehicle emissions control programs comprise more than just standards for new vehicles. It is just as important for regulators to focus on reducing emissions from the legacy or “in-use” fleet, especially to realize health and climate benefits in the near term. A single old diesel truck might pollute as much as dozens of new ones. Cleaning up or eliminating the old vehicles is therefore an obvious strategy for policy makers looking to achieve rapid emissions reductions.

Our recent report on controlling emissions from the legacy HDV fleet presents a broad overview of strategies available to national and local regulators. It covers five categories of in-use emission control solutions, with examples: targeting gross-emitting vehicles, using cleaner fuels, scrapping older vehicles, retrofitting high-emitting vehicles, and employing complementary strategies. For most regions, combining some or all of these policies through both mandatory and voluntary programs will be the most promising approach.

This report is the first item in what will be a steady stream of work the ICCT will be doing as a partner in the Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants (CCAC). The CCAC is a voluntary, collaborative global partnership of governments, intergovernmental organizations, the private sector, and civil society working together to urgently reduce emissions of black carbon and other short-lived climate pollutants. Diesel emissions from heavy-duty vehicles – both new and legacy – are one of the key targets of the coalition’s efforts. We’re looking forward to continuing to work with such a productive alliance in the coming months and years.

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