Transportation Models

Overview

SCAG develops and maintains state-of-the-art transportation models to support SCAG’s planning program. These models include:

Transportation Models

SCAG applies these models to forecast transportation conditions and resulting air quality.

Activity-Based Model

SCAG is the primary agency responsible for the development and maintenance of travel demand forecasting models for the SCAG region. SCAG has been developing and improving these travel demand forecasting models since 1967. SCAG applies the models to provide state of the practice quantitative analysis for the Connect SoCal Regional Transportation Plan/Sustainable Communities Strategy (RTP/SCS), the Federal Transportation Improvement Program, and air quality management plans. The regional model is also used to evaluate other transportation proposals within the region. The model is based on Caliper Corporation’s TransCAD modeling software and the latest generation of the Coordinated Travel – Regional Activity Modeling Platform. 

The SCAG travel demand process is composed of two main components: 

  1. The SCAG Activity-Based Model (ABM), which simulates daily activity participation and scheduling for individuals, with travel viewed as a derivative of out-of-home activity participation and scheduling decisions. 

  2. A network assignment loads vehicles onto appropriate facilities to produce traffic volumes, congested speeds, vehicle-miles traveled, and vehicle-hours traveled estimates for each of the five time periods. The SCAG travel demand modeling process is shown in Figure 1. A series of multi-class highway assignments simultaneously load the vehicle forecasted by the SCAG ABM, pre-calculated trip origin and destination input matrices (airport, seaport, inter-regional by passenger vehicles), and three classes of heavy-duty trucks from the Heavy Duty Truck model. 

SCAG Travel Demand Process

SCAG Model Validation Report

Subregional Modeling Program

SCAG’s Subregional Modeling Program is a cornerstone initiative designed to enhance the capabilities of SCAG-member agencies, transportation commissions, subregions, and Caltrans by providing sophisticated modeling data and technical support.  

The program promotes consistency among the various modeling agencies within the region, ensuring a unified, standard approach to transportation planning. By fostering a standard modeling framework, the program enhances the reliability, accuracy, and comparability of regional data, which is crucial for effective planning and policymaking. Consistency facilitates better coordination among agencies but and supports a more cohesive vision for the region’s development. 

SCAG’s Subregional Modeling Program also significantly reduces the cost and effort involved in creating or upgrading subregional models. The program assists agencies in overcoming common challenges associated with model development and maintenance by providing shared resources, technical expertise, and advanced modeling tools. This collaborative approach not only optimizes resource utilization but also accelerates the implementation of innovative solutions tailored to the region’s unique needs. 

By supporting informed decision-making and fostering a collaborative planning environment, the Subregional Modeling Program is vital in shaping a sustainable and resilient future for Southern California. Through this initiative, SCAG and its partners are better equipped to address the complexities of regional growth, transportation demands, and environmental sustainability, ultimately enhancing the quality of life for all residents in the region.