Case Study:

Portland, Oregon

Methodology

Overall Approach

The procedure employed in this study involves four basic steps: 1) determine the travel impacts of each alternative investment program, using Portland Metro's regional travel demand model; 2) estimate the direct user benefits for each program using STEAM; 3) project the economic benefits that flow from the direct user benefits using the REMI model; and 4) calculate the benefit cost ratio for each alternative. This procedure is illustrated in Figure 2.

Figure 2. Analysis Procedure

Only the user benefits concerned with freight movement and other business travel were considered to have impacts on the regional economy. These benefits include time, vehicle operating, and accident cost savings for truck traffic and for "on-the-clock" business travel. User benefits to highway automobile passenger travelers were also reported and were included in the benefit-cost analysis but not in the economic impact analysis.

The following additional impacts were not estimated, either because they were assumed to be small or were not viewed as relevant to the study. However, they could be measured with little additional effort:

• Reductions in emissions and energy use, as well as monetary valuation of these reductions (STEAM calculates these impacts);
• Project construction expenditures (these were ignored because their impact is short-term rather than permanent); and
• Impacts on the economy of cost savings to passenger travelers. While cost savings for passenger travel may effect the regional economy, the linkage is less direct than cost savings for business travel. Research is underway for National Cooperative Highway Research Program (NCHRP) Project 2-21, Economic Impacts of Congestion, to investigate the impacts of commuter benefits on business cost savings.

Finally, the following effects were not considered because they were difficult to quantify:

• Effects of the transportation improvement on attraction of new industries and tourists (according to local sources, these effects are expected to be small).
• Salvage values of the facilities constructed. A salvage (or residual) value is often calculated in benefit-cost analysis in order to compare with different lifetimes. Calculation of salvage values would have been complex because of the many different types of investments included in the I-5 analysis, and also would rely on uncertain assumptions about project lifespans.
• Land use impacts (these will be addressed in a future phase of the project).
• Transit benefits and costs. Some of the options included transit and TDM improvements. The magnitude of transit-related benefits was not estimated, except to the extent to which transit improvements reduced highway traffic volumes and the level of congestion.
• Congestion caused by accidents. Recent evidence suggests that non-recurring delay resulting from incidents is valued more highly than predictable delay (Small, Noland, Chu, and Lewis, 1999). Truck incidents may also have significantly larger time delay impacts than passenger vehicles. Good analytical procedures and data to measure these impacts, however, do not currently exist for the Portland region.
• Other truck-related congestion and congestion at interchanges. Traffic delays from truck-related congestion were estimated conservatively using generic "passenger car equivalent" values. Regional travel demand models, such as the Portland Metro model used as the basis for this study, are not sufficient to estimate localized changes in delays from traffic diversions and interchange improvements.

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