|Transportation Model |
SCAG develops and maintains state-of-the-art transportation models to support SCAG’s planning program. These models include:
These models are applied by SCAG to forecast transportation conditions and resulting air quality.
Trip-Based Model (Existing Travel Demand Model)
The Regional Travel Demand Model provides travel forecasting capabilities for the analysis of SCAG’s plans and programs. The trip-based model was Peer Reviewed in May 2011 and found consistent with the state-of-the-practice.
The Activity-Based Model (ABM) is a new generation of travel demand model. The AMB simulates daily activities and travel patterns of all individuals in the region, as affected by transportation system level of service. This new modeling system is designed to meet or exceed federal regulations and state laws/requirements.
Subregional Modeling Tool
The new Subregional Modeling Tool (SMT) greatly simplifies the creation of subregional models. The SMT fully automates the development of all aspects of a subregional model. The Tool is used by transportation commissions, counties, subregions, and cities wishing to create subregional models based on SCAG’s new Regional Model. The new Tool promotes model consistency between the Region’s various model agencies and greatly reduces the cost and effort required to create subregional models.
Heavy-Duty Truck Model
Southern California Association of Governments (SCAG) developed the Heavy Duty Truck (HDT) model to evaluate important policy choices and investment decisions. The HDT model is a primary analysis tool to support the goods movement policy decisions made by SCAG and regional stakeholders.
Air Quality Model
EMFAC2007 is an emission factors model developed by the Air Resources Board (ARB) for calculating emission inventories for vehicles in California. This is the emission model approved by the Environmental Protection Agency (EPA) for calculating vehicle emissions for conformity purposes in California.
|Subregional Modeling |
The goal of the Subregional Modeling Program is to provide modeling support and services to SCAG member agencies, transportation commissions, subregions, and Caltrans. SCAG recently developed the Subregional Modeling Tool (SMT) to enhance modeling support to member agencies. The new Tool streamlines the development of models for agencies wishing to create subregional models based on SCAG’s Regional Transportation Model. The new SMT promotes model consistency between the Region’s various modeling agencies and greatly reduces the cost and effort required to create subregional models.
About Subregional Modeling Tool
The resulting model provides subregions a consistent tool to evaluate their plans and to provide SCAG input into the RTP process based on a common set of assumptions and analytical methods. Currently three subregional models were built using the Subregional Modeling Tool including:
- North Los Angeles Model
- San Bernardino County Model
- Imperial County Model
In addition, several city level models and corridor studies were developed using the SMT.
Features of Subregional Modeling Tool
The SMT fully automates the development of all aspects of a subregional model and includes the following features:
- User friendly model interface;
- Automated routines for assisting model developers to create new sub-area models;
- Sub-routines to automatically create key model inputs; and
- The model interface allows the modeler to run only the needed portion of the modeling code, which significantly reduces model run times.
Subregional Modeling Tool Framework
The Subregional Modeling Tool is built directly on top of SCAG’s Regional Model’s computer code. The SMT uses the same basic model components as the Regional Model, with custom sub-routines to automate the development of the subregional model inputs. This ensures that model methods and results are consistent. In addition, the common model and data structure encourages sharing of model input data between agencies.
Documents & Resources
Final Report for the SCAG Subregional Model in TransCAD 5.0
User’s Guide for the SCAG Subregional Planning Model in TransCAD 6.0
|Trip Based Model |
The Regional Travel Demand Model provides travel forecasting capabilities for the analysis of SCAG’s plans and programs. The current trip-based model was developed and adopted for the 2012 Regional Transportation Plan/Sustainable Communities Strategy (RTP/SCS) analysis.
About the Trip Based Model
Network based transportation modeling is a mandated Federal Conformity Rules requirement. The trip-based model was Peer Reviewed in May 2011 and found consistent with the state-of-the-practice. Currently, this model is the only approved model for regional transportation plans and programs analysis within the SCAG Region.
Trip Based Model Features
SCAG’s trip-based model includes a very advanced mode choice component capable of forecasting all travel modes within the Region, including high-speed rail. Additional capabilities have been added to capture pricing and the travel effects of smart growth.
Trip Based Model Framework
The model runs on the TransCad software platform and is based on a four-step model structure, which includes trip generation, trip distribution, mode choice, and trip assignment.
Model Inputs Include:
- Transportation Analysis Zones (TAZs) (4,109 tier 1 zones, 11,267 tier 2 zones)
- Socioeconomic Data (population, employment, households, workers, school enrollment)
- Highway network (70,000+ street segments, posted speed, number of lanes, and functional classification)
- Transit network (2000+ routes/patterns, headway, service hours, fares, stop locations)
- Seaports (heavy duty trucks)
- Airports (passenger and cargo trips)
- External (interaction with other regions and pass-through trips)
Model Outputs Include:
- Vehicle trips
- Traffic volumes
- VMT by link and geographic areas
- Trips origin/destination
- Trip length
- Mode shares
- Transit boarding
SCAG Regional Travel Demand Model and 2008 Model Validation
SCAG Regional Travel Model Enhancement Program and 2008 Model Validation (Peer Review Report)
|Air Quality Modeling & Analysis |
SCAG staff is responsible for the Transportation Air Quality Conformity Determination on the Regional Transportation Plan (RTP) and the Regional Transportation Improvement Program (RTIP). These conformity responsibilities now include the new air quality standards for fine particulate matter (PM2.5) and 8-hour Ozone.
The recent passage of Sustainable Communities and Climate Protection Act of 2008 (SB 375) also gives SCAG a new area of responsibility. The purpose of SB 375 is to implement the state’s greenhouse gas emissions (GHG) reduction goals in the sector of cars and light trucks. This mandate requires SCAG to meet its per-capita GHG emissions reduction targets at two points in the future – 2020 and 2035.
About SCAG Air Quality
Air Basin in SCAG Region
Air Districts in the SCAG Region
8-hour Ozone Federal Non-Attainment Area
Particulate Matter2.5 (PM2.5) Federal Non-Attainment Area
Particulate Matter10 (PM10) Federal Non-Attainment Area
Nitrogen Dioxide (NO2) Federal Maintenance Area
Carbon Monoxide (CO) Federal Maintenance Area
The EMFAC model is developed by the California Air Resources Board (ARB) and is used to calculate on-road motor vehicle emissions and transportation conformity process. EMFAC 2011 is the most recent version of the model. For information about the EMFAC 2011 Model please refer to the California Air Resources Board.
Regional Emission Analysis: The transportation activity data used in the EMFAC model are Vehicle Miles Traveled (VMT) by ranges in speed for light and medium-duty vehicles and by air basins for heavy-duty trucks. The light and medium-duty vehicles, by ARB’s definition of vehicle class, are passenger cars, light-duty trucks, medium-duty trucks, and motorcycles. The activity data are based on the following output from the transportation model:
- Highway link information such as volumes, distance, and congested speed.
- Intra-zonal trips, average travel time and distance.
Transportation Conformity Analysis: Transportation conformity is required by the Clean Air Act section 176(c) (42 U.S.C 7506(c)) to ensure that federal funding and approval are given to highway and transit projects that are consistent with (“conform to”) the air quality goals established by a state air quality implementation plan (SIP). Conformity to the purpose of the SIP means that transportation activities will not cause new air quality violations, worsen existing violations, or delay timely attainment of the relevant National Ambient Air Quality Standards (NAAQS). Conformity applies to non-attainment and maintenance areas for the following transportation-related criteria pollutants: ozone, PM2.5, PM10, CO, and NO2.
Office of Transportation and Air Quality
ARB Formal Rulemaking Activity
|Heavy Duty Truck Model |
Southern California Association of Governments (SCAG) developed the Heavy Duty Truck (HDT) Model to evaluate important policy choices and investment decisions. The HDT model is a primary analysis tool to support the goods movement policy decisions made by SCAG and regional stakeholders.
About SCAG’s HDT
As part of 2012-2035 Regional Transportation Plan/Sustainable Communities Strategy (RTP/SCS), the HDT model focused on analytical needs to support project and policy planning in the following key areas:
- Port Access Improvements
- Clean Technology Truck Lanes
- Freight Facility Developments and Land Use Strategies for Goods Movement-Oriented Activity Centers (Inland Ports, Freight Villages, new inland warehouse, and distribution center locations)
- Air Quality/Conformity Analysis
- Economic Impact Analysis
- Operational Strategies (port and highway)
The model development process included a thorough review of the HDT model by an expert panel that ranged from academics to Consultants. The HDT model was validated by comparing the overall vehicle miles traveled (VMT) for individual counties and air basins against the data obtained from the Highway Performance Monitoring System (HPMS).
Click on the Features and Framework of SCAG's HDT Flow Chart for additional information.
The model documentation includes further information on the following topics:
- HDT Model Structure: The model forecasts trips for three HDT weight classes: light-heavy (8,500 to 14,000 lbs. gross vehicle weight (GVW); medium-heavy (14,001 to 33,000 lbs. GVW); and heavy-heavy (>33,000 lbs. GVW
- Internal HDT Model Development: This includes the development of all HDT trips that have both origins and destinations within the six-county modeling area.
- Port Model Development: This includes the port model development that predicts the HDT trips coming out of and going into the San Pedro ports, which includes the Port of Long Beach (POLB) and Port of Los Angeles (POLA).
- External HDT Model Development: This includes how the external HDT trips are captured in the HDT model that come into, go out of, and pass through the region.
- Intermodal Trip Tables: This includes how the intermodal trip tables were derived and integrated with the HDT model.
- Time-of-day Choice: This includes the derivation of time of day factors from various sources.
- HDT Model Calibration and Validation: This includes validation data, procedures and results from various performance measures.
Heavy Duty Truck Model Documentation
SCAG's Goods Movement Program seeks to optimize the region's transportation system through increases in economic efficiency, congestion mitigation, safety and air quality improvements, and enhancements to system security. In doing so, all modes of freight are being evaluated, ultimately resulting in a series of new recommendations and policies regarding infrastructure improvements. Click here, for more information of SCAG’s Goods Movement Program.
|Activity Based Model |
The Activity-Based Model (ABM) is a new generation of travel demand model. According to the 2010 RTP Guideline by California Transportation Commission, the largest four MPOs in California are encouraged to transition to activity-based travel demand models for the following RTP cycle (if the model is not already developed and validated for the current RTP cycle). This new modeling system is designed to meet/exceed federal regulations and state laws and requirements.
About SCAG ABM
SCAG’s ABM adopts a true activity-based approach by focusing explicitly on activity episode generation and their characteristics. Key model characteristics include:
- ABM creates rich socio-economic characteristics for each person and for each household in the SCAG region;
- Simulates daily activities and travel patterns of all individuals in the region, as affected by transportation system level of services;
- Predicts decisions “whether, when, where, for how long, with whom and in what sequence” to participate in activities;
- Simulates the effects of transportation and land development investments and policies on the quality (time and cost) and quantity (traffic volume, congestion, and vehicle miles traveled) of travel by different modes (walk, bike, transit, and auto); and
- Generates performance indicators, conformity analysis, and environmental justice analysis for the 2016 RTP/SCS. It is being developed to be capable of analyzing the impact of infrastructure investment, land use development, pricing policy, active transportation, high speed rail, and travel demand management.
Features of SCAG ABM
SCAG’s ABM incorporates a state-of-the-art approach to forecast travel behavior in a micro-simulation framework. Major strengths of SCAG ABM include: comprehensively characterizes the activity-travel patterns of all household members; incorporates spatial-temporal dependencies and constraints between and within individuals of a household; incorporates advanced vehicle type choice sub-model (vehicle fleet composition defined by body type, fuel type, make/model, and vintage) for emissions analysis; temporal and spatial resolutions; and involves a portable and flexible object-oriented software architecture design.
SCAG ABM Framework
SimAGENT (Simulator of Activities, Greenhouse Emissions, Networks, and Travel) is the base framework of SCAG’s ABM. It includes three core modules:
- PopGen - Generates complete synthetic population by expanding the disaggregate sample data to mirror known aggregate distributions of household and person variables of interest;
- CEMSELTS - Creates additional variables for each individual and simulates long-term choices; and
- CEMDAP - Simulates activity schedule and travel characteristics for each individual of the region.
Documents & Resources
Flow Chart Sequence of SimAGENT Modules and their interactions
SCAG Activity-Based Model Development Workshop PresentationModeling Task Force Presentation
Stage 1 Model Development Reports
SimAGENT Final Report 1 - Overview
SimAGENT Final Report 2 - Opportunity-Based Dynamic Accessibility Indicators in SimAGENT
SimAGENT Final Report 3 - Population Synthesis
SimAGENT Final Report 4 - Activity-Based Travel Demand Analysis
SimAGENT Final Report 5 - TRANSIMS and MATSIM Experiments in SimAGENT
SimAGENT Research Papers
A Joint Vehicle Holdings (Type and Vintage) and Primary Driver Assignment Model with an Application for California
A Methodology to Match Distributions of Both Household and Person Attributes in the Generation of Synthetic Populations
A Household-Level Activity Pattern Generation Model for the Simulator of Activities, Greenhouse Emissions, Networks, and Travel (SimAGENT) System in Southern California
Simulator of Activities, Greenhouse Emissions, Networks, and Travel (SimAGENT) in Southern California
The Application of a Socio-Economic Model System for Activity-Based Modeling: Experience from Southern California
TMIPTMIP Activity-Based Modeling Webinars
University of TexasCEMDAP and CEMSELTS’s Developer’s Website
SCAG DTA Model Development & Training