Four-Step travel demand modeling is the traditional procedure utilized for transportation forecasts.
Step 1: Trip Generation – How many trips are generated?
The goal of trip generation (production) is to estimate the number of trips that are produced or originate in each Traffic Analysis Zone (TAZ). A set of equations is used to estimate the number of trips produced by and attracted to each zone based on its residential and employment characteristics. For example; the more employment a zone has, the more work trips it attracts. The more retail employees in a zone, the more shopping trips are assumed to be attracted there
Step 2: Trip Distribution – Where do trips go?
This is the second component, where matches between origins and destinations are developed. Trip ends are linked to create complete trips. This can occur within the same zone, or between adjacent zones with varying distance. For example; trips between residential neighborhoods in West Pasco to employment cents in north Richland.
Step 3: Mode Choice – What travel mode is used for each trip?
Mode Choice predicts the choices that individuals or groups make in selecting their transportation modes. An important objective is to predict the share of trips attracted to public transportation. This is new to BFCG travel demand modeling. Other factors considered for mode choice include: travel time, travel cost and access to mass transit options.
Step 4: Trip Assignment – What is the route of each trip?
The final step is to determine the routes travelers choose to reach their destinations. With the 2015 model, the regional transportation network was updated, along with the addition of many network connectors. Network connectors are used to represent the local streets/access routes. For example, a congested corridor might change the route of a user to take a different route with a longer distance but same travel time. This assists with the analysis of new or future transportation projects or improvements.
Note on the 2015 Regional Travel Demand Model
The BFCG currently utilizes the TransCAD Transportation Planning Software, developed by the Caliper Corporation.