Travel

Caltrans - District 3
Transportation Planning and Local Assistance

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Office of Travel Forecasting and Modeling

The Office of Travel Forecasting and Modeling is a functional unit under the Deputy District Director of Planning and Local Assistance. The primary function of the Office provides critical project travel analysis of past, present and future traffic volumes, turn movements as well as other operational characteristics.

Additionally, this Office performs several technical analysis on this data in order to identify and articulate traffic and roadway efficiencies and deficiencies. These mobility measures are used as the major stepping-stone through Project Approval and the Environmental Documentation, thus bringing the project closer to actual construction.

The Office of Travel Forecasting also has several technical tools through which they define traffic conditions. They include:

Four step Modeling Process
Micro-modeling
Stick Diagrams
Traffic Counts
Traffic Indexes
Transportation Concept Report (traffic data only)
Highway Capacity software and manual

Terms and Definitions

Four Step Modeling Process
The process in which four key components are taken into consideration when developing a view of traffic from a macro standpoint:

Trip Generation
This submodel translates land use quanities and household demographics in each "travel analysis zone" (TAZ) into person trip ends by trips purpose using trip generation rates for each land use variable.
Trip Distribution
This submodel is used to forecast the number of trips from one zone to each other zone, in each trip purpose. This is based on factors that relate the likelihood of travel between any two zones to the travel time (or cost) between the two zones.
Mode Choice
This estimates the proportions of the total person trips, which use the available modes for travel between each pair of zones. Depending on the regional model available, modes can include car, bus, light-rail, train, bicycle, walk, truck, etc.
Trip Assignment
Determining the path or route that the trip maker is taking from one zone to another on the travel network.

Click here to see an example of a macro model.

Modeling: Defined
A mathematical and/or geographical tool used to analyze, describes the transportation system under vaious conditions and scenarios.

Demand Modeling
The data environment and graphical interface that expresses travel conditions from a larger or "big picture" perspective. This type of software is generally used to analyze large mainline or corridor projects.

Micro-modeling
The data environment and graphical interface that expresses traffic and roadway conditions from a smaller or "small picture perspective. This type of software is best used to analyze intersections or small geographical areas.

Micro-Simulation
A micro-simulation enables the modeler to enter traffic data into the system then view that traffic in a simulated environment.

Click here for an example of a simulation.

Stick Diagrams
The static representations of the past, present and future traffic volumes and turn movements for a given project-area.

Click here to for an example of a stick diagram.

Traffic Counts
The process by which traffic data is gathered or in the field by people as well as other mechanical vehicle counters. The actual data is then applied to the various static or dynamic modeling software such as those listed above.

Traffic Indexes
A series of calculations and other data that makes up a profile of the present and future traffic for a given area. The volume, composition, and cumulative axial loading of traffic will have a deleterious affect on the pavement over a given number of years. The Traffic Index will determine the depth that the pavement needs to be in order to accommodate that particular makeup of traffic in that area.

Transportation Concept Report (Traffic Data)
The Travel Forecasting portion of this report involves developing a profile of the traffic and roadway system by identifying characteristics such as shoulder width, lane width, type grade-line as well as traffic makeup.

Highway Capacity Manual Analysis
When a roadway analysis is performed, the Highway Capacity Manual analysis is a nationally recognized system of policies and procedures that is widely considered the "standard" in both analysis methodology and conclusions.