Definition of Terms
2.1 Definition of Terms
Refer to the SIDRA GLOSSARY for definitions of a broad range of road traffic analysis terms.
A · B · C · D · F · G · I · M · O · R · S · T · U · W · Z
A
All-or-Nothing (AON) Assignment
All-or-Nothing Assignment is a traffic assignment method that loads all Trips onto a single shortest Route between Origin and Destination, wherein the shortest Route is based travel times (costs) for an Assign Network with Initial Vehicle Volumes and Fixed Route Trips already loaded.
ASSIGN (SIDRA ASSIGN)
SIDRA ASSIGN (also used as ASSIGN or Assign) is the name of the lane-based multimodal traffic assignment functionality in SIDRA INTERSECTION. See SIDRA ASSIGN (ASSIGN).
Assign Network
A SIDRA Network with special data for Traffic Assignment, which include Zones, Origin - Destination (O-D) Volumes, Fixed Routes and traffic assignment parameters in addition to all the functionalities of a Basic Network.
Assign O-D Volume
An Assign O-D Volume (by Movement Class) refers to the number of Assign Trips between Origin-Destination (O-D) pairs. See Origin - Destination (O-D) Volume.
Assign Route
An Assign Route is the Route between an Origin-Destination pair that is used by an Assign Trip. Assign Routes are determined by a traffic assignment principle, such as Wardrop's First Principle of Traffic Equilibrium.
Assign Scenario
Assign Scenario defines the demand volume for an Assign Network. It includes the O-D Volume and the Initial Vehicle Volumes for Network Sites.
Assign Trip
Assign Trips are Trips that have the flexibility to find and use alternative Routes to go from an Origin to a Destination. See Fixed Route Trip (Fixed Trip), Trip.
Attraction (Attracted Trips)
The sum of all Trips that are attracted to a Destination Zone. See Generation (Generated Trips).
B
Basic Network
A SIDRA Network with full Network model functionalities except Traffic Assignment. See Assign Network.
C
Column Trip Matrix
A type of Trip Table wherein each O-D Pair (first two columns) and its number of Trips (next column) are in the same row of the table. See Trip Matrix.
Consistency Index
Consistency Index is a measure of convergence of a traffic assignment solution. It is an indicator of the consistency between of the Route flows and Route travel time (cost) of the traffic assignment solution. It is calculated as the percentage difference between the Assign Trip Total Travel Time (Cost) based on the estimated Route travel time (cost) given a set of Assign Route flows; and the Assign Trip Travel Time (Cost) based on the estimated Assign Route flows given the same Route travel time (cost). The Convergence Index approaches zero when the Route flows and Route travel time (cost) of the traffic assignment solution are mutually consistent. See Duality Gap.
D
Desire Line
A Desire Line is a line drawn connecting two Zones to illustrate the number of Trips between them. The width of the Desire Line can be scaled according to the number of Trips.
Destination Zone
Destination Zone is the end point of a Trip. See Origin Zone, Zone.
Duality Gap
Duality Gap is a traffic assignment measure of convergence. It is an indicator of how close the traffic assignment solution is to satisfying Wardrop's First Principle. Duality Gap is the percentage difference between the total trip travel cost and the theoretical total trip travel cost assuming lowest travel cost for all trips. The Duality Gap approaches zero the closer the solution is to satisfying Wardrop's First Principle. See Consistency Index.
Dynamic Traffic Assignment
A traffic assignment method which permits the Trip Matrix to vary in terms of both level and pattern of O-D demand volumes during the modelled period. See Traffic Assignment.
F
Fixed O-D Volume (Fixed Trip Matrix)
An O-D Volume matrix for Fixed Trips where the travel demand volumes on user-specified Routes between O-D pairs remain constant regardless of changes in Route travel times or costs.
Fixed Route
Fixed Route is a Route specified by the user with a number of Trips between an Origin - Destination pair. Assign Trips can also use a Fixed Route.
Fixed Route Assignment (FRA)
Fixed Route Assignment is a traffic assignment method that loads Trips to user-specified Routes with user-specified proportions (i.e. uses Fixed Trip Proportions). See All-or-Nothing (AON) Assignment, Incremental Assignment (IA), Stochastic User Equilibrium (SUE) Assignment, User Equilibrium (UE) Assignment.
Fixed Route Trip (Fixed Trip)
A Trip that will be assigned to a user-specified Fixed Route between its Origin and Destination Zones defined for representing Movement Classes such as Bus, Tram / Light Rail and regulated Truck trips that are restricted to use a specific Route. See Assign Trip.
Fixed Trip (Volume) Proportion
Proportion of a Fixed Route Trip volume to the Total Fixed Trip volumes between an O-D pair. See Fixed Route Assignment (FRA).
Furness Method
A balancing technique to estimate a Trip Matrix from another Trip Matrix using specified growth factors so that the row and column totals match projected future totals for Trip Generation and Attraction.
G
Generation (Generated Trips)
The sum of all Trips that are generated at an Origin Zone. See Attraction (Attracted Trips).
I
Incremental Assignment (IA)
A traffic assignment method that loads Origin-Destination (O-D) demand volumes onto a Network in successive increments, updating Route travel times (costs) after each increment before loading the next. See All-or-Nothing (AON) Assignment, Fixed Route Assignment (FRA), Stochastic User Equilibrium (SUE) Assignment, User Equilibrium (UE) Assignment.
Initial Vehicle Volumes
Initial Vehicle Volumes in ASSIGN are static background traffic volumes at specified Sites (intersections, crossings, interchanges, arterial and freeway segments) that are loaded first before any Trips are loaded in the Assign Network.
Interzonal Trip
A Trip whose Origin and Destination are not the same Zone. See Intrazonal Trip.
Intrazonal Trip
A Trip whose Origin and Destination are the same Zone. See Interzonal Trip.
M
Matrix Estimation
The method to adjust input Trip Matrices so that, when assigned, the resulting intersection flow rates accord more with known intersection flow rates.
O
Origin - Destination (O-D) Preset
A set of O-D Pairs used to filter SIDRA ASSIGN Outputs. See Origin - Destination (O-D) Volume.
Origin - Destination (O-D) Volume
The volume of Trips between an Origin - Destination (O-D) pair, which may include Assign Trips and Fixed Route Trips. See Trip Matrix.
Origin Zone
Origin Zone is the starting point of a Trip. See Destination Zone, Zone.
R
Route
A complete path consisting of a series of movements in one direction of travel between Origin and Destination in a Network. See Assign Route, Fixed Route.
S
SIDRA ASSIGN (ASSIGN)
SIDRA ASSIGN (also used as ASSIGN or Assign) is the name of the lane-based multimodal traffic assignment functionality in the SIDRA INTERSECTION software. See ASSIGN (SIDRA ASSIGN).
Stochastic User Equilibrium (SUE) Assignment
Stochastic User Equilibrium Assignment (SUE) is a traffic assignment method that apportions Trip demands to alternative Routes based on probabilistic route choice preferences during the loading process. This method is based on the assumption of drivers' different perceptions of travel times (costs). This is the default method used in SIDRA ASSIGN. See All-or-Nothing (AON) Assignment, Fixed Route Assignment (FRA), Incremental Assignment (IA), User Equilibrium (UE) Assignment, Travel Time Coefficient.
T
Traffic Assignment
A method used to estimate the specific Routes taken by road users between given Origin Zones and Destination Zones, effectively turning an O-D demand matrix to traffic volumes on individual roads and intersections. It excludes all demand responses other than Route choice. See All-or-Nothing (AON) Assignment, Dynamic Traffic Assignment, Fixed Route Assignment (FRA), Incremental Assignment (IA), Stochastic User Equilibrium (SUE) Assignment, User Equilibrium (UE) Assignment.
Travel Time Coefficient
Travel Time Coefficient is the multiplier of the Route Travel Time (Cost) variable of a linear utility function for a Route, which is used in the context of Stochastic User Equilibrium (SUE) Assignment.
Trip
Trip is unit traffic demand (vehicle) from an Origin Zone to a Destination Zone. A Trip can either be an Assign Trip or Fixed Route Trip.
Trip Matrix
Trip Matrix is a table containing the O-D Volumes. Also called Origin-Destination (O-D) Matrix or Trip Table. In SIDRA ASSIGN, the rows represent Origin Zones and columns represent Destination Zones. See Column Trip Matrix.
U
User Equilibrium (UE) Assignment
User Equilibrium is a deterministic traffic assignment method that apportions Trips to Routes according to Wardrop's First Principle of Traffic Equilibrium. See All-or-Nothing (AON) Assignment, Fixed Route Assignment (FRA), Incremental Assignment (IA), Stochastic User Equilibrium (SUE) Assignment.
W
Wardrop's First Principle of Traffic Equilibrium
The user equilibrium principle for traffic on a Network, stating that for each Origin - Destination (O-D) pair, the travel times (costs) on all used Routes are equal and less than those which would be experienced on any unused Route. This reflects drivers choosing Routes that minimise their travel time (cost). See User Equilibrium (UE) Assignment, Duality Gap.
Z
Zone
Zone (Traffic Zone) is a designated point in an Assign Network that can serve as a Trip Origin and/or Trip Destination. See Zone Connector.
Zone Connector
Zone Connectors are links between Zones and External Legs of an Assign Network that load Trips from Origin Zones onto the Network and connect Trips from the Network to Destination Zones. A Zone Connector does not contribute to Route travel distance, time or cost and it has unlimited capacity.