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Step 4: Develop and Evaluate Base Year Conditions and a Reference Case


Before a metropolitan area develops and evaluates alternative scenarios for its future, it is important to understand existing conditions and the likely outcomes of its currently adopted plans. In this step, information about existing or recent conditions in the planning area are compiled to create a base year conditions report. Growth forecasts from existing plans are then added to the base year conditions to develop a “reference case” for the selected planning period. Key products of this step are a technical report and a report card. They show both performance today and how well current plans are expected to perform in achieving various objectives, including reducing GHG emissions, by the end of the planning period. The development and evaluation of the base year conditions and the reference case are useful for engaging decision-makers, advisory committees, and the public in discussions about potential strategies for the future, which would be tested later in the alternative scenarios.


Scenario planning starts with developing an understanding of current conditions, or “where the metropolitan area is today,” and then evaluating the likely results of existing plans and policies in a reference case. Use of Metropolitan GreenSTEP to perform an early high-level strategic assessment of conditions in the base year and the outcomes of the reference case is recommended before embarking on a more detailed analysis utilizing a sketch planning tool.

The base year conditions (or current conditions) are the conditions that exist in the metropolitan area in the base year (determined as part of Step 3), including factors related to population, employment, mix of land uses, transportation system, travel patterns, infrastructure, etc. This step involves assembling the information about base year conditions and building a base year conditions report as the benchmark for comparison with the reference case and alternative future scenarios. Using the data and information collected in Step 3, a base year can be described and modeled in Metropolitan GreenSTEP, with the results providing a benchmark accounting of today’s transportation behavior and GHG emissions.

The reference case is the default or starting point for developing future scenarios. It is an estimate of where current adopted land use and transportation plans are likely to lead the metropolitan area over the selected long-term planning period.

Baseline assumptions include assumptions about future conditions likely to affect people’s travel habits. These include estimates about the price of gasoline, forecasts about future vehicle technologies, and estimates about expected state and federal policies and programs, including state and federal funding for transportation.

The process includes the use of evaluation measures (identified in Step 2) that indicate how well the metropolitan area is doing – and is expected to do in the future – in terms of such things as housing affordability, jobs-to-housing balance, amount of open space, and GHG reduction. This information is presented to the community as a report card. This report card provides an opportunity to engage stakeholders in a discussion about where the community is heading based on current trends, and identify key issues or problems that the community may want to explore further.

Base Year Conditions

A crucial element of scenario planning is estimating a metropolitan area’s base year conditions, which provides a known reference point. As discussed in Step 3, the recommended base year is 2005, unless more current comprehensive data are available. Measuring what conditions are like today (in the agreed upon base year) makes it possible to describe the future in comparative terms that make sense to people.
Build the Base Year Conditions
Oregon’s metropolitan areas have a wealth of data available related to housing units, households, commercial uses, employment and existing transportation networks. These datasets form the backbone of defining the base year conditions. However, this data needs to be organized and translated before using it in a sketch planning tool. Use of the sketch planning tool then allows for a visual representation of the base conditions. The result is an accurate, realistic and visually displayed base year, often referred to as the “virtual present” for the metropolitan area. This virtual present is now in a format that can be easily compared to the reference case and future alternative scenarios built in Step 5.

Due to the availability of data and consistency with the baseline year for the adopted GHG reduction targets, the recommended base year is 2005, which should be used unless a different base year was selected in Step 3.

To build base year conditions for use with a sketch planning tool, or other GIS-based methods, translate what is on the ground in the adopted base year into a GIS layer by applying the building blocks described in Step 3. Paint the building blocks on the GIS base layer in the sketch planning tool by matching the building block types as closely as possible to the existing land use on the ground, that existed in the base year. The process can be automated by simply assigning building blocks based on comprehensive plan designations and TAZ numbers. Although the automated method can be refined and adjusted, the manual method is typically more accurate - but time consuming. Each of these methods is explained in further detail in a sidebar to the right and in the Technical Appendix.
Understand Base Year Conditions
Once the base year conditions have been compiled, the next task is to analyze them. Documenting the base year conditions provides a point of reference for comparing future conditions in the reference case and in any alterative future scenarios developed later. Results of the analysis will include the outputs of Metropolitan GreenSTEP, the sketch planning tool and any other models used. For example, by documenting how many miles the average household traveled in 2005, the evaluation of future scenarios can report how much more or less households are expected to travel in the future planning year.

Reference Case

The reference case builds from the base year conditions to forecast how today’s plans and policies are likely to play out in the future planning year. The reference case will reflect future development consistent with current local comprehensive plans.

The reference case developed with Metropolitan GreenSTEP will show the likely results of current plans on GHG emissions and other evaluation criteria in the future planning year. The reference case expressed through the sketch planning tool illustrates future conditions based on comprehensive plans, using the population and employment allocations included in the adopted RTP.
Build the Reference Case
The initial run of Metropolitan GreenSTEP, described in Step 3, provided an estimate of where the metropolitan area may be in the future planning year based on various policies. Metro’s Climate Smart Communities initiative used this approach, with staff developing variations on likely future outcomes for analysis through Metropolitan GreenSTEP, in order to see how outcomes might vary if anticipated vehicle and fuel technology changes occur at a different rate than expected.

Metropolitan GreenSTEP incorporates detailed assumptions about state and federal policies, and other assumptions, expected to be in place over the planning period (as described in Step 3 and the Technical Appendix). Metropolitan GreenSTEP accounts for the combined effect of all these factors to estimate a series of transportation related outcomes, including GHG emissions.
Evaluate the Reference case
The reference case is initially evaluated using outputs from Metropolitan GreenSTEP and subsequent outputs from the sketch planning tool. The recommended approach for applying these two tools together involves three analysis phases already detailed in Step 3. First, conduct a high-level strategic assessment with Metropolitan GreenSTEP. Second, develop detailed scenarios with a sketch planning tool. And third, further evaluate the scenarios by running Metropolitan GreenSTEP a second time. The outcomes of the reference case evaluation should be organized and interpreted based on the reductions of GHG emissions from transportation, the metropolitan area’s own evaluation criteria and other community objectives developed in Step 2.

The evaluation criteria generally focus on results described in quantifiable terms that provide a basis for comparing outcomes of different scenarios. These evaluation criteria may include jobs to housing balance, vehicle miles traveled, land consumption, housing and jobs mix and GHG emissions. Comparing the reference case to the base case, using a consistent set of evaluation criteria from Step 2, will provide important perspective for community residents and stakeholders in understanding the magnitude of the changes anticipated. Evaluating the reference case in this way will answer the important question of where the metropolitan area is likely headed in terms of GHG emissions reduction and other community objectives.

The evaluation of the base and reference cases provides the first set of answers to the overarching questions about how the metropolitan area is doing and where things are headed based on current plans. A wealth of evaluation data will have been produced. With this new information the project enters a new phase – sharing the numbers from the evaluation among staff, elected officials and with community members.

Share the Base Year Conditions Report and Reference Case Evaluation

The outcomes of Step 4 can be used to tell a story about the community’s future based on current trends. This task now involves communicating that information in a compelling manner. The evaluation criteria provided a way to evaluate the performance of that scenario. The next step is to engage the community in a dialogue and lay the groundwork for developing alternative scenarios.
Technical Report and Presentation
The technical report presents the work done in Steps 1 through 4, including evaluations of the base year and the reference case scenario, based on the evaluation criteria from Step 2 and the adopted targets for 2035. The report should describe the scenario process used, illustrate the base conditions and reference case scenario, and include an assessment of how the base year and reference case scenario performed against the criteria.

The report should then identify proposed techniques that may help the community achieve its vision, values and goals (as described by the guiding principles and the evaluation criteria) and measurable GHG reductions. These techniques are tested in Step 5. The outputs of Metropolitan GreenSTEP are used here to identify potential land use, transportation, economic, and environmental policy options that seem to be working or are not working as expected. Outputs include estimates of vehicle ownership, vehicle travel, fuel consumption, and GHG emissions at the individual household level. This information will be useful in engaging people in the development of the alternative scenarios in Step 5.

Presenting this information in a manner that translates the technical findings into everyday language and concepts is an important task; doing this effectively will help illuminate choices for the public and decision makers. A summary report card can also be an effective tool to summarize and convert complex technical information into meaningful communication material.
Public Engagement Materials
At this point in the process, a portrayal of what the future may hold based on the plans and practices of today should have emerged. For many, it will be the first time they have seen estimates about how their communities might be different in the future and how it might affect them in their daily lives - such as the costs of housing and transportation, or how future growth patterns may affect nearby farms, forests and open spaces.

The analysis and lessons learned in this step should form the basis of a public engagement effort that occurs for the most part in Step 5. To create a report card, use the guiding principles established in Step 1 to help group the evaluation findings in ways that will resonate with the community. The results of the base year and reference case evaluations can then be reframed into a more useful communications material, with messages that link to the guiding principles, to encourage people to be involved in alternative scenario development in Step 5.

While the technical report should describe all of evaluation measures employed, a smaller set of evaluations should be used during public engagement, either by consolidating concepts or by drawing out the issues of most interest. There is no magic number of measures that should be presented in the report card. Rather, the task involves selecting a few key results from the analysis which can interesting and helpful in making the process meaningful to the public.


Development of the base case and the reference case provides a key starting point for stakeholder and public dialogue to consider options for the future. Documenting base year conditions gives the decision-makers and the public a clear picture of current conditions, and an assessment of whether things are likely to get better or worse in the future – either in the reference case or in the different alternative scenarios that are developed in the next step. Using Metropolitan GreenSTEP in the beginning, before more detailed sketch planning, provides a high-level assessment of the reference case and the likely outcomes from existing adopted plans. With this information in hand, communities are positioned to consider ways land use and transportation plans and policies might be changed to create a better future for the community and also meet GHG reduction targets and goals.