County government, SANDAG is the metropolitan planning organization and council of governments for the San Diego, California, region. In addition to the regular members of SANDAG’s board, advisory members from other entities in and around San Diego also participate in SANDAG activities; these include neighboring governments (Imperial County, California, and the Mexican government), transportation authorities (Caltrans, the San Diego Metropolitan Transit System, and the North County Transit District), and the U.S. Department of Defense (given the large presence of Naval Base San Diego and other military facilities in the region). In addition to serving as the San Diego region’s designated census data center, SANDAG focuses on issues of major regional impact such as air quality/environmental planning, housing development—and transportation planning.
Jarosz described region-level transportation planning as a multistep process, beginning with identifying stakeholders and assessing their needs and goals. Her particular focus, transportation modeling, is the basis of the next few steps: developing a set of alternatives from available data and information, using them to predict outcomes, and testing and evaluating them in order to select a final alternative. The analytic work in transportation modeling helps with the next immediate step—budgeting for the work—and then implementing. Planning agencies then have the responsibility to evaluate whether the chosen alternative has done what it was intended and expected to, and amend the plans as necessary. In theory, she noted, the final step is achievement of a finished, “perfect” transportation system; in practice, as she noted, anyone who has ever been stuck in traffic knows that the perfect transportation system is a constantly moving target. Consequently, planning agencies like SANDA Grepeat this process every several years (often a 4-year cycle), trying to map out transportation infrastructure needs 20–40 years into the future.
Focusing on the transportation modeling steps in this general process, Jarosz presented a simplified outline of the transportation modeling process, with specific reference to the points where ACS data and products enter the mix; this general structure is shown in Figure 2-2. Similar to the general health care planning process described by Thomas in Section 2–C, the first step is preparation of demographic and economic profiles for the area and populations of interest, and then trying to forecast future trends in the population. In transportation, there is interest in the population, housing, and jobs in the region in the next few decades, and the ACS is an important source of those data. Particular variables of interest include household structure (headship), group quarters characteristics, school enrollment, and housing structure type preferences (single versus multifamily or mobile home). In a region like San Diego, with its military presence, information and forecasts on the active-duty military personnel (and their dependents) are particularly important. These demographic and economic characteristics—the data that enter the forecast models—are obtainable from the ACS summary tables or from analysis of the ACS PUMS files.