There are many ways to improve air quality and reduce the climate-forcing impacts of vehicle use. Often overlooked in discussions of advanced vehicle technology and alternative fuels are the various approaches that can impact the existing stock of in-use vehicles. Whereas new vehicle manufacturer developments and new standards for vehicles, low-sulfur fuels, and low-carbon fuels are enormously beneficial in the long term, they do not so fundamentally alter the older stock of much higher polluting vehicles that are on the road for 10 to 20 years on average.
This paper focuses on ways to reduce the emissions of the in-use vehicle fleet, with particular emphasis on heavy-duty diesel trucks, due to their disproportionate contribution to both urban air quality and greenhouse gas emissions. The report surveys measures that are in effect across the world, including programs that help identify vehicles that disproportionately contribute to overall emissions; administer inspection, maintenance, and in-use emission testing protocols to help eliminate gross-emitting vehicles; assist in the effective deployment of retrofit emission control technology; and promote improved fuel quality to directly reduce emissions and facilitate improved emission control technology.
The work highlights a number of national, regional, and local examples of effective emission control programs that exhibit best practices from around the world. The report concludes by summarizing the critical actions that can be undertaken at national and local levels to install world-class emission control programs for in-use heavy-duty vehicles.