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Aimsun Next Travel Demand Modeling

The capabilities of Aimsun Next for Travel Demand Modeling are based on the Four-Step Transport Planning Methodology.

The four-step model is based on trips aggregated by transport zone. The four stages are:

  1. Generation/Attraction: Stage 1 determines what trips originate in each zone and terminate in each zone based on the population and land use of each zone.
  2. Distribution: Stage 2 matches trip origins and destinations.
  3. Modal Split: Stage 3 estimates the mode choice that travelers use for these trips allocating trips to transit or private transport.
  4. Assignment: The final assignment stage models the trips on the transport network and evaluates travel times and costs.

This methodology is applied iteratively, as results from step four provide improved input to feed back to steps two and three.

Model Management

The main procedures in the Travel Demand Modeling are managed with Scenarios and Experiments A generic Four-Step process diagram editor is available to manage the work flow of the process, connecting all the steps through outputs and inputs. Refer to the Four-Step Model Scenario Section

Generation Attraction

A Generation / Attraction Scenario and Experiment takes socioeconomic and land use data as its input and produces trip numbers for the zones in the model.

Distribution

The Distribution step is either determined by using Furnessing techniques to factor growth in a matrix or by using either a Gravity Model or a Departure Destination Choice Model in a Distribution Experiment as part of a Distribution Scenario.

The Modal Split step is managed by the Modal Split Experiment in a Modal Split Scenario.

Assignment

The Macroscopic Modeling functionalities cover the later stages of the Four-Step Transport Planning Methodology.

The main functions are:

Static Traffic Assignment (Single-User and Multi-User), Demand Analysis (including Matrix import and export, Matrix manipulation, Matrix Balancing, Detector Location Analysis, and Static OD Adjustment) and Static Traversal Generation.

Static Traffic Assignment

Static Traffic Assignment assigns traffic to the road network, evaluates the performance of the network as drivers modify their routes and returns the time and cost of each trip. Static Traffic Assignment is managed by the Static Assignment Experiment, which is located inside a Static Assignment Scenario

Static OD Adjustment

Static OD Adjustment adjusts OD demand matrices using an a priori matrix and observed data from traffic counts. Static OD Adjustment is managed by the Static OD Adjustment Experiment, which is located inside a Static OD Adjustment Scenario.

Static OD Departure Adjustment

Static OD Departure Adjustment creates a time profiled demand from a static demand. It is managed by the Static OD Departure Adjustment Experiment, which is located inside a Static OD Departure Adjustment Scenario.

Static Traversal Generation

Static Traversal Generation is used, once a static assignment experiment has been executed and a subnetwork has been defined to generate a matrix of trios traversing the subnetwork. It is accessed, by right-clicking on the subnetwork listed in the Project window under the Subnetworks folder.

Transit Assignment

Transit Assignment assigns passengers in a Traffic Demand to the Transit Lines. The output is the transit loading for each line.

Transit Adjustment

Transit Adjustment adjusts the passenger demand matrix to calibrate it to the observed Transit loads.

Matrix Operations

Matrices can be imported or exported from ASCII and Excel files by copying and pasting the data. Matrix manipulations and operations are available from the Edit menu of the matrix. Refer to the OD Matrix Editing section.

Matrix Balancing is based on the Furness algorithm and is used to modify a prior matrix in order to satisfy the new generation/attraction totals. This feature is accessible via the OD Matrix Editor as one of the operations that can be applied to a matrix, the Furness operation.

Detector Location

The Detector Location feature can be used to evaluate the relevance of the current detection sites locations and to work out an improvement to the current configuration by proposing new detector locations. It is located in the Infrastructure folder in the Project Window.

Supernodes

Supernodes are only used in macroscopic models. They are used to represent situations in which it is not possible to model the cost of traversing the sections and turns by the sum of the individual components. Supernode creation is explained in the Node Editing Section

Licenses

Users with an Aimsun Next Advanced Edition license can access:

  • Static Assignment Scenarios and Experiments
  • Static OD Adjustment Scenarios and Experiments
  • Static OD Departure Adjustment Scenarios and Experiments
  • Transit Assignment Scenarios and Experiments
  • Transit OD Adjustment Scenarios and Experiments

Users with an Aimsun Next Pro TDM or an Expert Edition License can access, in addition to the above:

  • Generation/Attraction Scenarios and Experiments
  • Distribution Scenarios and Experiments
  • Modal Split Scenarios and Experiments
  • Four-Step Model Scenarios and Experiments