DOI: http://dx.doi.org/10.1065/ehs2001.06.010 - - -
Intention, Goal, and Scope. An indicator or metric is proposed to reflect the environmental and resource impacts of passenger vehicles. Primarily intended to assist consumers in purchasing decisions, the metric is designed to provide timely, relevant and meaningful information that captures most of the environmental impacts occurring throughout the vehicle life cycle. The paper presents the criteria for such metrics, reviews the relevant literature, demonstrates the metric for the model/year 2000 vehicles, and discusses the use, evolution and limitations of the indicator. - - - Background. Vehicles are significant emitters of air pollutants and a major influence on the environment. The life cycle of a vehicle results in many environmental and resource impacts, some of which can be difficult and/or controversial to evaluate. While several eco-indicators have been developed, a need exists for comprehensive, objective and comparative information to describe the environmental impacts of vehicles on a brand/model basis. Such information can increase the consumer awareness of a vehicle\""s environmental performance, as well as the automobile manufacturer\""s corporate governance, product planning and marketing practices. - - -
Methods. Environmental performance criteria for vehicles are developed using principles of life cycle assessment (LCA), methods used to define eco-indicators, and available or reasonably obtainable and quality-assured data. Previous LCA studies are reviewed to help formulate the suggested metric. These studies are consistent in showing that the vehicle use phase (including fuel production) currently accounts for most emissions of greenhouse gases as well as most of the conventional pollutants.
In the suggested metric, estimates of in-use emissions are combined using a weighting based on LCA results and an estimate of the severity of impacts. Emissions of the four regulated and conventional pollutants are given half of the total score and each receives equal weight. This approximates the population in regions not in compliance with US air quality standards, i.e., emissions of ozone-forming pollutants nitrogen oxides (NOx) and non-methane hydrocarbons (NMHC) together represent 25% of the score, and emissions of toxicants carbon monoxide (CO) and particulate matter (PM) each represent 12.5%. Recognizing the potential magnitude and consequence (but also great uncertainties) of impacts related to energy consumption and greenhouse gas (GHG) emissions, carbon dioxide (CO2) and other GHG emissions receive a larger weighting, 40% of the total. The pollutant and energy efficiency scores, which are proportional to the reduction in emissions from a baseline year 2000 vehicle, are based on emission certifications, and highway and city fuel economy estimates. In addition, the vehicle-related solid waste generation and resource consumption, which is based on the percent recycled content in the vehicle, is given the final 10% of the score. At present, the recycled content of vehicles is not available on a brand/model basis, however, this information is not difficult to determine. Scores for advanced technology vehicles, e.g., electric vehicles, are derived in a manner consistent with conventional gasoline and diesel-powered vehicles.
The relative ranking or weighting of emissions can be based on many factors, and the uncertainty and ultimately the subjectivity of any weighting system is recognized and discussed at length. Nonetheless, the suggested indicator incorporates meaningful measures of environmental impacts. Further, it is clearly definable, consistent, verifiable, transparent and understandable to vehicle purchasers and other stakeholders. For these and other reasons discussed in the paper, the indicator can provide valuable information for both purchasing decisions and improvement analyses. - - -
Results. The 200 brand/models and 1,450 engine/drive train configurations in the 2000 model year demonstrate a large range of emissions, e.g., greenhouse gas |
