Land Use Model

Primary Purpose

The PECAS (the Production, Exchange and Consumption Allocation System) Model for the SCAG Region was constructed in 2010 as a technical tool to assist in the development of Regional Transportation Plan (RTP) and policy decision making process. According to 2010 RTP guidelines, MPOs shall operate a regional economic and land use model that is sensitive to transportation scenarios such that the effects of land use and transportation policies can interact with feedback in an integrated transportation and land use modeling system.

PECAS Framework

PECAS is a generalized approach for simulating spatial economic systems (Hunt and Abraham, 2003).  The modeling framework incorporates a nested logic model utilizing two PECAS modules and two non-PECAS modules. The four modules are described below:

  • Activity Allocation (AA) module simulates a series of choices for households and industries: where to operate; what kind of technology options to use and where to buy and sell products.
  • Space Development (SD) module simulates a series of choices for parcel developers, such as:
    • No change, demolish, add, renovate, derelict or new constriction
    • Optimal size of addition or new construction
  • Transport (TR) module is a non-PECAS module which represents the transportation system and provides the yearly description of the disutility of movement between locations that underlie activity interaction.
  • Economic Demographic (ED) module is a non-PECAS module that develops aggregate economic forecasts for the study area. These forecasts include projected numbers of household by category and employment by type (as indications of expected economic activity) for a horizon year.

The system works through time in a series of time steps, from one point in time to the next with the AA Module and the SD Module considering the period from each point in time to the next. Interaction among modules simulating temporal dynamics:

About SCAG's PECAS Model

SCAG intends to use the land use model to inform the RTP/SCS growth forecasting process at the jurisdictional level and potentially at the Tier 1 Transportation Analysis Zone level (4,109 zones cover the entire SCAG region). The model system has an aggregate equilibrium structure with separate flows of exchanges (including goods, services, labor, and space) going from production to consumption. Click here for the PECAS Model Design Diagram.

The PECAS Model

  • Forecasts developmental patterns as well as home and business locations, economic interactions and economic performance in the future.
  • Provides a guide to socioeconomic forecasts under constrained conditions (assuming development will happen within the current general plan), and unconstrained condition (assuming development can happen as economically suitable).
  • Provides region-wide impact analysis for policy scenarios.
  • Example model outputs include: VMT Tax – Difference of Households from Baseline (Figure 5) and VMT Tax – Difference of Jobs from Baseline (Figure 6).

Modeling Documentation

Presentation on SCAG PECAS Land Use Model Development
Presentation on Spatial Input-Output Models: PECAS (Webinar 4 of an 8-part TMIP Webinar Series)
Design and Application of the PECAS Land Use Modeling System
PECAS Software User Guide
PECAS File Interchanges
PECAS Theoretical Formulation
PECAS System Documentation and Technical Notes - Modeling Status and Next Steps
PECAS Diagram