In many regions of the world, older, high-emitting vehicles account for a small percentage of the overall vehicle fleet but a disproportionately large share of total emissions. It is estimated that these vehicles may be responsible for more than 50% of particulate matter (PM) and black carbon (BC) emissions by 2020 (Yan et al., 2011). There are a wide variety of emission control programs designed to reduce emissions from these legacy, high-emitting vehicles. Vehicle replacement, retrofit, and repower programs can have an immediate and positive environmental impact because they reduce emissions from older, gross emitting, and inefficient vehicles in the fleet within a short period of time. Positive environmental impacts can be achieved with the reduction of gaseous pollutants (CO, HC, NOX), as well as of particulate matter. Greenhouse gas (GHG) emissions are also reduced, especially of short-lived climate pollutants (SLCPs) such as black carbon, one of the main components of PM emissions. While a region considering one or more of these types of programs should fully assess which would be most cost-effective based on the region’s specific capabilities and needs, this report focuses primarily on vehicle replacement programs. Vehicle replacement programs seek to entirely replace older and gross emitting vehicles with newer, more efficient, and environmentally friendly vehicles. This report
evaluates vehicle replacement programs worldwide and suggests five best practices that serve as guidelines for policymakers seeking to design and implement these programs in their jurisdictions.