Travel Demand Modeling

Introduction

The Alamo Area Metropolitan Planning Organization (AAMPO) develops and maintains a full set of Travel Demand Models (TDMs) for the region. The TDM efforts cover all of Bexar, Comal, Guadalupe, Kendall and Wilson Counties. For our on-going 2025 TDM update, all of Medina and a small portion of Atascosa will be added to the modeled area. The TDMs provide the primary means for identifying existing and future transportation system deficiencies and for assessing proposed regional mobility improvements. The models are suitable for the following applications:

• Analysis of Transportation Systems for Short and Long Range Planning
• Evaluation of Regional Transportation System Improvements
• Identification of Transportation System Deficiencies
• Conducting Alternatives Analyses, Corridor Studies or Subarea Studies
• Providing Traffic Statistics for estimating Highway Performance Metrics
• Interfacing with US EPA Emissions Software (MOVES-Motor Vehicle Emissions Simulator) to Estimate On-road Mobile Source Emissions for Urban Airshed Modeling and AQ Conformity Analyses

The current TDM, known as San Antonio Multimodal Model, version 5.2 (SAMM5.2) is being updated (to SAMM5.3) for improved results and ease of operation. The models also incorporate a new Master Network System that improves project tracking and project annotations required for Air Quality Conformity analyses as well as a new network editing process. Another SAMM5.3 improvement is the addition of an automated Traffic Assignment Adjustment process that provides alternative projected volumes (including by four time periods) that dampen modeled volume extremes, such that very high or very low volumes are adjusted (based upon available historical individual network link count data). SAMM5.3 will be used for evaluating alternative demographic scenarios as well as alternative highway and transit systems as part of the Transportation Improvement Process (TIP) and the Metropolitan Transportation Plan (MTP).

AAMPO’s TDM is a traditional 4+ step model (which now includes 6 steps) including (1) Network and Input Data Preparation, (2) Trip Generation (Tripcal6), (3) Trip Distribution (Destination Choice), (4) Mode Choice (Nested Logit), (5) Traffic and Transit Assignments (TransCAD Multi-Modal, Multi-Class User Equilibrium) and (6) TDM Data output tailored to required Air Quality and Proposed Project metrics. The current SAMM assignment models execute individual traffic assignments for each time period, which are then combined to produce 24-hr daily (weekday) traffic volumes. The model also features Speed Feedback and produces time-of-day directional forecasts for 4 daily time periods: AM-Peak, Midday, PM-Peak, and Overnight. This speed feedback process produces traffic forecasts in a state of equilibrium, such that quicker, alternative network trip routes do not exist.

The SAMM 5.3 TDM (expanded to 6+ counties) will be calibrated and validated to 2025 travel data (including 2022 Household Travel Survey, 2023 On-board Transit Survey and current Spring season 2025 Traffic Count and Transit Boarding data). The models will produce a Short-Range Forecast for 2030, as well as forecasts for 2035, 2045, and 2050. AAMPO will also procure 2024 and 2025 LOCUS Data (location based daily travel pattern data) to further refine the model performance.