UC Davis Institute of Transportation Studies

Planning agencies, analysts, non-profit organizations, regulatory and legislative bodies, and other organizations develop long-range local, state, regional, and national transportation plans. These plans typically comprise two or more alternatives, or scenarios. These alternatives have different financial costs and different impacts on travel, air quality, noise, safety, and so on. To evaluate and compare these alternatives with their different impacts, planners and analysts often use social cost-benefit analysis (CBA), which estimates the dollar value of all of the major impacts of the plan on society. With social CBA, the different plan alternatives can be compared by the single metric of net dollar benefits.

In support of social CBAs of transportation plans, I have developed an Excel Workbook, called the "Social Cost Calculator," or SCC. The SCC estimates costs for up to five different transportation scenarios for up to six different geographic areas, in the following cost categories:

* public-sector goods and services (e.g., highway maintenance and repair, highway patrol * climate-change * external costs of oil use (e.g., supply disruptions, military defense of oil supplies) * fuel cost (resource cost, taxes, producer surplus, and costs of delay) * noise * accidents * parking * travel time and congestion * air pollution from motor-vehicle exhaust * air pollution from the upstream lifecycle of fuels * air pollution from road dust, brake wear, and tire wear

For the most part, the categories listed above comprise all of the major social costs of motor-vehicle use except those that are efficiently paid or borne directly by motor-vehicle users such as vehicle costs, most operating costs, and some time costs. I exclude those efficiently priced costs for two reasons: i) because they are priced, they are relatively easy to estimate; and ii) because they are more or less efficiently priced, they are of no concern in an analysis of efficient use of transportation systems, and arguably are of only secondary concern in a social CBA. (They are of secondary concern in a social CBA if one believes that net private benefits per mile are likely to be similar across transportation scenarios, and consequently that differences in net social benefits among transportation scenarios are likely to be determined by differences in unpriced or inefficiently priced costs.)

Many but by no means all of the social costs listed above and estimated here are what economists call "external" costs, which can be understood to be inefficiently priced costs of motor-vehicle use (for details, see report # 9 in the UCD social-cost series). Air pollution, noise, congestion, climate change and some of accident, public-sector, oil-use, and fuel-use costs are externalities. Costs that are not directly related to motor-vehicle use (e.g., highway capital costs and defense expenditures), costs that are unpriced but not necessarily inefficiently so (e.g., bundled costs such as parking), and costs that are priced but not necessarily perfectly (e.g., highway maintenance costs and fuel costs), are social costs and may or may not be denominated "external" costs depending on one's tastes.

Social costs, which include all external costs plus all non-external costs, are used in social CBA, because in social CBA one wishes to compare all of the costs and benefits to society, for each alternative. Social and external costs also are relevant to pricing and hence are useful in analyses of efficient use of transportation modes. Thus, social and external costs inform our comparison of alternative transportation plans and our policies for efficient use of transportation systems.

This report documents the data and methods used in the SCC, and applies the SCC to a case study of Sacramento. The Sacramento Council of Governments (SACOG) develops alternative transportation plans for Sacramento as part of its Metropolitan Transportation Plan (MTP). Here, we apply the SCC to estimate the social costs of five different MTP alternatives (four for the year 2025, and a year-2000 baseline), for the six counties in the SACOG planning area. As part of this case study, parameter values pertinent to Sacramento are documented throughout. Note: