Vehicle emissions created or removed by a project are counted as benefits or disbenefits.
Examples
- A traffic artery is widened, increasing the vehicle miles traveled (VMT) for the street, but decreasing vehicle-hours on this and other streets.
- A transit system converts from diesel buses to compressed natural gas buses, reducing emissions.
- A vanpool program is created, reducing the number of vehicle trips.
Approach
To assign a dollar value to the benefits of a project:
- Choose an appropriate dollar value per unit of emissions.
- Estimate the changes in vehicle-miles, vehicle-hours and vehicle-trips for different classes of vehicles. Use a model to estimate the change in emissions that will result from the project.
- Based on the estimate, calculate the project's benefits.
To prioritize projects that would reduce emissions:
- Determine the cost of each project.
- Estimate the change in vehicle miles traveled (VMT), vehicle-trips, and vehicle-hours that will result from each project.
- Calculate the cost of the project per unit of emissions.
Emissions from motor vehicles cause significant damage to the environment and to human health. People who are exposed to high levels of emissions may suffer from respiratory disease, lung damage, or even cancer. Emissions can also reduce visibility, and cause lower crop yields in agricultural areas. They contribute to global climate change as well—a more remote but perhaps more serious threat.
All motor vehicles in use today, whether they run on diesel fuel, gasoline, or an alternative fuel like compressed natural gas, create emissions. Even electric cars, trains, and buses are responsible for emissions, since the electricity they use is often generated by burning coal or other fossil fuels. Using electric vehicles merely changes the location affected by the emissions. Because the emissions are located at a power plant rather than distributed across many different roads, some argue that emissions control can be more easily effected.
Most benefit-cost analyses of emissions focus on the effects of air pollution on human health, since these are better understood and therefore easier to quantify. An analysis typically considers the following types of emissions:
- Carbon monoxide (CO): A gas that reduces the ability of blood to carry oxygen
- Nitrogen oxides (NOx): Compounds, some of which are toxic, that combine with VOC in sunlight, causing ozone to form
- Sulfur oxides (SOX): Lung irritants that contribute to acid rain
- Volatile organic compounds (VOC): Compounds, some of which are toxic, that combine with NOx in sunlight, causing ozone to form
- Fine particulates (PM10): Very small particles that can be inhaled and damage the lungs
Regardless of whether a project will increase or reduce emissions, a benefit-cost model can be used to estimate any change in emissions and calculate its positive or negative benefit. For projects that reduce emissions, the cost-effectiveness of several projects can be compared by finding the cost of each unit of pollution reduction.
Emissions also have other environmental effects that are more difficult to quantify. These should be acknowledged in the project analysis even though they cannot be included easily in a benefit-cost ratio.
Sources
Booz-Allen & Hamilton Inc. California Life-Cycle Benefit/Cost Analysis Model (Cal-B/C) Technical Supplement to User's Guide. California Department of Transportation (Caltrans), 1999. Available at: http://www.dot.ca.gov/hq/tpp/tools_files/tech_supp.pdf.
Burmich, P. "Methods to Find the Cost-Effectiveness of Funding Air Quality Projects." California Environmental Protection Agency Air Resources Board and California Department of Transportation (Caltrans), 2003. Available at: http://www.arb.ca.gov/planning/tsaq/eval/hc03v2.pdf
Delucchi, M., J. Murphy, J. Kim, and D. McCubbin. "The Cost of Crop Damage Caused By Ozone Air Pollution From Motor Vehicles." Institute of Transportation Studies, University of California, Davis, report UCD-ITS-RR-96-3 (12), 1996.
Forkenbrock, D. J., and L. A. Schweitzer. "Environmental Justice in Transportation Planning." Journal of the American Planning Association 65(1), 1999, pp. 96-111.
McCubbin, D. R., and M. A. Delucchi. "The Social Cost of the Health Effects of Motor-Vehicle Air Pollution." Institute of Transportation Studies, University of California, Davis, report UCD-ITS-RR-96-3 (11), 1996.
Murphy, J., and M. Delucchi. "A Review of the Literature on the Social Cost of Motor Vehicle Use in the United States." Journal of Transportation and Statistics. January 1998 , pp. 15-42.
Small, K. A., and C. Kazimi. "On the Costs of Air Pollution from Motor Vehicles." Journal of Transport Economics and Policy XXIX(1), 1995, pp. 7-32.
Zhou, H., and D. Sperling. "Traffic Emission Pollution Sampling and Analysis on Urban Streets with High-Rising Buildings." Transportation Research Part D 6, 2001, pp. 269-281.