Traffic Assignment Model

The traffic assignment model ('traffic_assignment') can be used to calculate traffic flows on a transport network dataset. Internally it uses Aequilibrae to calculate traffic flows. The model merely acts as a wrapper.

Dataset requirements

The traffic assignement model expects a dataset with a certain set of entity groups and attributes.

virtual_node_entities. These are the incoming and outgoing nodes of the network and contain the

origin destination matrices. The OD-matrices must be a CSR-type float matrix attribute. Every value represents the outgoing demand (in vehicles/hour) from the row’s virtual node to the virtual node matching the column. Two OD-matrix attributes are supported:

  • transport.passenger_demand

  • transport.cargo_demand

virtual_link_entities. These connect virtual_node_entities to transport_node_entities using

the connection.from_node_id and connection.to_node_id attributes

transport_node_entities. these are nodes in the network and connect transport segments to

other transport segmenets and to virtual links

The transport segments entity type depends on the modality the model operates. These can be either

  • road_segment_entities for roads

  • waterway_segment_entities for waterways

  • track_segment_entities for railway tracks

Supported attributes for the transport segments are:

  • transport.capacity

  • transport.layout (a 4-tuple indicating number of lanes an directionality: [forward lanes, reverse lanes, bidirectional lanes, unknown directionality lanes])

  • transport.max_speed

Modalities

The traffic assignment model can operate in different modes, depending on the modality. They are as following

Roads

For roads, the model supports both passenger demand and cargo demand. Model parameters that can be tweaked are vdf_alpha, vdf_beta and cargo_pcu. vdf_alpha and vdf_beta in the volume delay function the volume on the road is calculated by combining the passenger vehicle volume and the cargo vehicle volume for which the cargo vehicle volume has a weight equal to the cargo_pcu parameter.

Other modalities

Other modalities are waterways, cargo_tracks and passenger_tracks. These will be explained further in the future

Example Configuration

{
  "name": "road_traffic_assignment",
  "type": "traffic_assignment",
  "dataset": "some_road_network",
  "modality": "roads"
  "vdf_beta": 0.64,
  "vdf_alpha": 4.0,
  "cargo_pcu": 1.9
}

Traffic Assigment Model Config Schema Reference

TrafficAssignmentConfig

type: object
properties:
dataset: string the name of a transport network dataset (required)
modality: string one of waterways, cargo_tracks or passenger_tracks (required)
vdf_alpha: number the alpha parameter of the volume delay function (default: 4.0)
vdf_beta: number the beta parameter of the volume delay function (default: 0.64)
cargo_pcu: number the weight factor of a cargo vehicle (truck) on the volume (default: 1.9)