- Regional Demographic Trend Projection
- County Demographic Trend Projection
- City Demographic Trend Projection
- Baseline Growth Forecast
- Policy Growth Forecast
Regional Demographic Trend Projection
Projections of baseline population and households at the regional level are the yardsticks for evaluation of the data gathered through input from jurisdictions to produce the socio-economic data sets used for transportation modeling.
SCAG uses a standard demographic cohort-component model to project population at the regional level. The components are fertility, mortality and migration. Projections are derived for 18 age cohorts in five years intervals for the projection timeline.
The SCAG cohort-component model computes the population at a future point in time by adding to the existing population the number of births and persons moving into the region during a time interval, and by subtracting the number of deaths and the number of persons moving out of the area. Fertility, mortality and migration rates are projected in 5 year intervals for each age group, for four mutually exclusive ethnic groups: Non-Hispanic White, Non-Hispanic Black, Non-Hispanic Asian and Hispanic, by these population classes: residents, domestic migrants and international migrants.
A second phase links population dynamics to economic trends, and is based on the assumption that patterns of migration into and out of the region are influenced by the availability of jobs. The future labor force is computed from the population projection model. Projected labor force participation rates are applied to the working age population. This labor force number is compared to the number of jobs projected by the shift/share economic model. If any imbalance occurs between the two figures, it is corrected by adjusting the migration assumptions of the demographic projection model.
SCAG projects regional households by using the projected headship rate. The projected households at a future point in time are computed by multiplying the projected population by the projected headship rate. The headship rate is the proportion of a population cohort that forms a household. It is usually specified by age, gender, and ethnicity. Headship rates are projected in 5 year intervals for each age group, for four mutually exclusive ethnic groups.top of page
County Demographic Trend Projection
As used in the regional baseline population and household projection, SCAG uses the cohort-component model and the headship rate to project the county baseline population and households. The sum of the county trend projections is compared to the regional independent projections. If the results are significantly divergent, input data at the county level is adjusted to bring the sum of counties projection and the regional independent projections more closely in line. Complete agreement between the two projections is not mandatory. After analysis, the sum of counties constitutes the regional baseline projections.top of page
City Demographic Trend Projection
SCAG projects city level demographic trend projections using the housing unit method, which is one of the most widely used methods for estimating and projecting local area households and population for planning purposes. The housing unit method consists of the following four procedures. First, occupied housing units (households) are estimated by extrapolating the past trend of occupied housing units. Second, household (residential) population is estimated by multiplying occupied housing units (households) by the projected average household size. Third, projected group quarters population is added to projected household population. Fourth, projected total population of local jurisdictions are adjusted or smoothed out in order to maintain its consistency with the projected County population.top of page
Baseline Growth Forecast
The regional growth totals were derived by analyzing historical population, housing and economic trends, and incorporating the future demographic rates and employment shift-share assumptions. The Baseline also incorporates recent local input, as described below in the description.
The baseline growth forecast for the 2008 RTP represents the most likely growth distribution in the absence of any explicit regional policies. In addition to historical demographic trends and future projections, the following recent local input reflecting current general plans and local policies were considered and incorporated:
- Imperial County: the 2035 consensus total population, household, and employment growth projections at traffic analysis zone (TAZ) and city levels agreed upon by SCAG, IVAG, and Caltrans District 11.
- Los Angeles County: the 2035 total population, household, and employment growth projections at census tract and city levels provided by subregions/cities.
- Orange County: the Adopted 2006 OCP 2035 total housing and employment projections at census tract, city, and county levels as submitted by OCCOP.
- Riverside County: the 2006 RCP 2035 total population, household, and employment projections at census tract, city, and county levels provided by Riverside County Transportation and Land Management Agency (RCTLMA). This agency collected city level/census tract level input from local jurisdictions in Riverside County as agreed upon by RCTLMA, WRCOG, and CVAG.
- San Bernardino County: the 2035 household and employment projections at census tract, city, and county levels provided by SANBAG.
- Ventura County: the 2035 total population, household, and employment growth projections at census tract and city levels provided by VCOG.
In addition, the technical forecast at the regional level presented to Plans and Programs Technical Advisory Committee in March 2006 was used as a reference to ensure technical consistency and integrity of major variables–population, employment, household–built upon a bottom–up process which summed up all local/subregion projections.top of page
Policy Growth Forecast
The development of the Policy Growth Forecast began with the workshop scenario. It relies on focusing growth toward existing and planned regional centers and transit areas. It also assumes more mixed use development types to encourage increased transit use and non-motorized transportation alternatives. It reflects the input incorporated into the workshop scenario, including reintroducing some of the lower density, primarily single-family uses strategically throughout the region.
The 2008 RTP Policy Growth Forecast reflects an application of the Compass Blueprint Principles, yielding significant transportation benefits. It relies on focusing growth toward existing and planned regional centers and transit areas. It also assumes more mixed use development types to encourage increased transit use and non-motorized transportation alternatives. It reflects the input incorporated into the workshop scenario, including reintroducing some of the lower density, primarily single-family uses strategically throughout the region.
- Presentations and Maps
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