Definition of Terms

All-or-Nothing (AON) Assignment

All-or-Nothing Assignment is a traffic assignment method that loads all Trips to the shortest path, wherein the shortest path is based on an Assign Network with only Initial Volumes and Fixed Route Trips loaded.

Assign Network

A Network with special data for traffic assignment, which includes Zones, Origin-Destination Volumes, Fixed Routes and traffic assignment parameters.

Assign O-D Volume

An Assign O-D Volume is a matrix of Assign Trips between Origin-Destination (O-D) pairs.

Assign Route

An Assign Route is the route between an Origin-Destination pair that is used by an Assign Trip.

Assign Scenario

Assign Scenario defines the demand volume for an Assign Network. It includes the O-D Volume and the Initial Volumes.

Assign Trip

Trips that use routes that determined by a traffic assignment principle, such as Wardrop’s First Principle of Traffic Equlibrium.

Attraction

Attraction or Attracted Trips is the sum of all trips that go to a (Destination) Zone.

Basic Network

Basic Network is a SIDRA Network Model that is used as the basis for creating an Assign Network.

Destination Zone

Destination Zones are the end point of Trips.

Desire Line

A Desire Line is a line drawn connecting two Zones to illustrate the number of Trips between them. The width the Desire Line can be scaled according to the number of Trips.

Duality Gap

Stochastic Duality Gap is a measure of convergence of the User Equilibrium method. It is an indicator of how close the solution is to the solution is to satisfying Wardop’s First Principle. Duality Gap is the percentage difference between the total trip travel cost and the theoretical total trip travel cost assuming shortest travel cost for all trips. The Duality Gap approaches zero the closer the solution is to satisfying Wardop’s First Principle.

Fixed Route

User-defined route between an Origin-Destination pair that is used by a Fixed Trip.

Fixed Route Assignment (FRA)

Fixed Route Assignment is traffic assignment method that loads trips to user-defined routes.

Fixed (Route) Trip

A trip that has a user-defined route between its Origin and Destination Zone. Fixed Trips are useful for representing bus and tram trips.

Fixed O-D Volume

A Fixed O-D Volume is a matrix of Fixed Trips between Origin-Destination (O-D) pairs.

Fixed Trip (Volume) Proportion

The Fixed Trip Proportion is the Fixed Route’s share of the total Fixed Trips between an O-D pair.

Furness Method

A method to estimate a Trip Matrix from another Trip Matrix that simultaneously satisifes user-given growth factors for Generation and Attraction.

Generation (or Generated Trips)

Generation is the sum of all trips from an Origin Zone.

Incremental Assignment (IA)

Incremental Assignment is a traffic assignment technique where trips are loaded in small proprotions on the network.

Initial Volumes

Initial Volumes in ASSIGN are Site Volumes that are loaded first before any Trips are loaded in the ASSIGN Network. Initial Volumes represent static background traffic volumes.

Intrazonal Trips

Trips whose Origin and Destination is the same Zone.

Origin Zone

Origin Zones are the starting point of trips.

Origin-Destination (O-D) Preset

An O-D Preset is a set of O-D Pairs that is defnined for an Assign Volume Bin. An O-D Preset is used to filter ASSIGN Outputs.

Origin-Destination (O-D) Volume

An O-D Volume is a matrix of Trips between Origin-Destination (O-D) pairs, which includes Assign and Fixed Trips.

Stochastic Duality Gap

Stochastic Duality Gap is a measure of convergence of the the Stochastic User Equilibrium method. It is an indicator of the consistency between of the route flows and route travel cost of the traffic assignment solution. It is calculated as percentage difference between the Network Travel Cost based on output (or estimated) route travel cost given a set of Assign route flows; and the Network Travel Cost based on output (or estimated) route flows given the same route travel cost. The Stochastic Duality Gap approaches zero when the route flows and route travel cost of the traffic assignment solution are percectly consistent with each other.

Stochastic User Equilibrium (SUE)

Stochastic User Equilibrium Assignment (SUE) is an assignment method that apportions trips to alternative routes based on a probabilistic route choice preference.

Travel Time Coefficient

Coefficient of the Route Travel Time variable of a utility function for an alternative route. Refer to Stochastic User Equilibrium (SUE) assignment method for context.

Trip

Trip is unit traffic demand from an Origin Zone to a Destination Zone. A Trip can either be an Assign Trip or Fixed Trip.

Trip Matrix

An O-D Volume is often presented in a Trip Matrix, which is a table wherein the row headers are Origin Zones and column headers are Destination Zones. The values in the cells of a Trip Matrix is the number of Trips between the corresponding Origin and Destination Zone.

User Equilibrium (UE)

User Equilibrium is an assignment method that aportions trips to routes that satisfies Wardrop’s First Principle.

Wardrop’s First Principle of Traffic Equlibrium

Traffic arranges itself on networks such that the cost of travel on all routes used between each Origin-Destination pair is equal to the minimum cost of travel and all unused routes have equal or greater cost.

Zone Connector

Zone Connectors links a Zone to one or more External Legs of an ASSIGN Network. A Zone Connector can be one-way or two-way. Zone Connector does not contribute to route travel distance, time or cost and it has unlimited capacity.

Zones

Zones (or Traffic Zones) are designated points in an ASSIGN Network that serve as trip ends. Zones can be an Origin and/or Destination.