An integrated assessment of climate mitigation policy, air quality and traffic safety for passenger cars in the UK

Climate change mitigation policies applied to passenger cars can be effective in reducing tailpipe CO₂ rates by changing vehicle mass, fuels, and drive-train technology. However, these same factors can lead to changes in vehicle emissions, vehicle safety, and, consequently, changes in health outcomes from air pollution and traffic collisions. These relationships are examined using the UK as a case study where tax regimes based on tailpipe CO₂ emission rates have been in place since 2001. Policymakers are tasked to design CO₂ policies for passenger cars, but the effectiveness of new policies will depend on how well climate mitigation is balanced with other relevant risks. I examine the rationale and introduce the basic framework for an Integrated Assessment approach to quantitatively assess passenger car CO₂ policies. As industrialized countries transition to more heterogeneous fleets with increasing uptake of alternative fuels and technologies, the importance of decision criteria choices, risk metrics, system boundaries, and inclusion of all relevant risks using an Integrated Assessment framework will be increasingly critical. Since 2001, there has been a strong growth in diesel car registrations in the UK. For 2001-2020, I estimate that switching from gasoline to diesel cars reduces CO₂ emissions by 0.4 mega-tonnes annually. However, current diesel cars emit higher levels of PM10 and the switch from gasoline to diesel cars is estimated to result in 90 additional deaths annually (range 20-300) from 2001-2020. The UK has also had an increase in registrations of lighter vehicles. The relationship between tailpipe CO₂ emission rates, vehicle mass, and traffic safety risks were examined. The two-car “first law” fatality risk ratio for drivers of lighter cars relative to drivers of heavier cars was estimated to be the mass ratio raised to the power 5.3. Independent estimates of driver killed or serious injury risk in two-car collisions were found to be inversely related to vehicle CO₂ emission rates. Scenario analyses show that policies combining incentives for lighter cars with a 1,600 kg upper limit for new cars should simultaneously achieve traffic safety and climate mitigation goals more effectively than policies with no upper limit on mass.Science, Faculty ofResources, Environment and Sustainability (IRES), Institute forGraduat