Overview
1 Overview
1.1 How to Use This User Guide
This User Guide has four sections.
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Section 1 - Overview describes SIDRA ASSIGN including its core capabilities as a modelling tool and the network configurations that can be modelled by ASSIGN.
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Section 2 - Concepts and Terminology describes the traffic assignment concepts applied in ASSIGN. It also defines the terminologies used in the user interface and reports. Use this Section as reference for a basic understanding of the inputs, parameters and methods used by ASSIGN. This Section does not go into the theoretical details of traffic assignment, and the readers keen to learn more about traffic assignment theory are directed to other technical documents and reports (see References).
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Section 3 - User Interface describes the ASSIGN User Interface. It describes features of the User Interface. Use this Section as a reference on scope, content and key functionalities of ASSIGN Dialogs, Reports and Displays.
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Section 4 - Steps to Use SIDRA ASSIGN illustrates the basic steps to create and process an Assign Network. This Section is a useful reference for first-time users of ASSIGN.
1.2 What is SIDRA ASSIGN?
SIDRA ASSIGN (short name: ASSIGN) is a detailed lane-based multimodal traffic assignment module integrated with the SIDRA Network Model (Table 1.1.1). Traffic assignment is the determination of the Routes taken by road users between given Origin and Destination (O-D) Zones. In the process of Route selection, road users interact with road users from other origins and destinations as they aim to find routes that would minimise their travel time or cost. Traffic assignment uses Trips by O-D Pair to estimate Site movement volumes. ASSIGN uses the movement travel times determined by the SIDRA Network Model.
SIDRA ASSIGN is useful for assessing the impacts of traffic management schemes that result in changes in Routes used by road users, especially when there are available alternative routes. ASSIGN is also useful to analyse any SIDRA Network Model wherein Trip O-D Volumes are known, instead of Network Site Volumes.
You can use ASSIGN for detailed analysis of critical Network areas using O-D Trip Matrix data from macroscopic strategic planning software. ASSIGN can also be used for special application to enable easy use of pre-built SIDRA Network Templates to model paired intersections, interchanges, two-stage crossings, and alternative intersections and interchanges. SIDRA ASSIGN will determine internal approach movement volumes.
SIDRA ASSIGN uses Route Travel Times based on the SIDRA lane-based micro-analytical multi-modal Network traffic model as an integral part of its traffic assignment model. It translates the Approach Movements at Network Sites into a Movement Network for each Movement Class which includes Light Vehicles, Heavy Vehicles, Buses, Bicycles, Large Trucks, Light Rail / Trams and six User Classes. Routes generated by ASSIGN are formed by connecting Network Site Movements by Movement Class. Trips between Origin and Destination for a Movement Class need to have at least one viable Route of interconnected movements for the Movement Class. If there is more than one viable Route, ASSIGN will allocate Trips to Routes according to the specified traffic assignment method.
Table 1.1.1 — Key Features of SIDRA ASSIGN
| User given Route volumes between Origin - Destination | Programmatically determined equilibrium of Route volumes between Origin - Destination | |
|---|---|---|
| Detailed traffic interaction at intersections | SIDRA ASSIGN (microanalytical) | SIDRA ASSIGN (microanalytical) |
| No or simple traffic interaction at intersections | - | - |
SIDRA ASSIGN is capable of the following traffic assignment methods:
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Stochastic User Equilibrium Assignment (SUE) probabilistic Route choice preferences based on drivers' different perceptions of travel times (costs). This is the default method in SIDRA ASSIGN.
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User Equilibrium (UE): deterministic method to implement Wardrop's first principle: no user can reduce travel time by switching Routes (Wardrop 1952, Akçelik 1979).
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Fixed Route Assignment (FRA): user-defined Route volume proportions for known Route choice patterns.
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Incremental Assignment (IA): progressive loading of demand volumes to observe congestion build-up.
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All-or-Nothing (AON): baseline loading to the lowest travel time (cost) Route.
Fixed Routes can be used in conjunction with other assignment methods which is useful in representing Buses, Trams, Trucks or Bicycles. The modeller also has the option to include static background approach movement volumes in traffic assignment.
SIDRA ASSIGN is a powerful traffic assignment model that combines the detailed micro-analytical modelling capability of the SIDRA NETWORK Model and traffic equilibrium assignment. ASSIGN can analyse the effects of complex traffic interaction at intersections and Route choice behaviour.
1.3 Scope of SIDRA ASSIGN
SIDRA ASSIGN is suited for modelling a small to medium size Network or corridor - the critical areas where the detailed lane-based SIDRA Network Model determines the quality of the traffic assignment process and the resulting output.
The following are the maximum numbers of ASSIGN Network elements:
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50 Zones per Assign Network,
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8 Zone Connectors per Zone (one Zone Connector per External Leg),
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20 Fixed Routes,
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12 Movement Classes (six Standard, six User Defined),
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50 O-D Volume sets per Assign Volume Bin.
SIDRA ASSIGN was introduced in SIDRA INTERSECTION Version 11 and accessing input and output data as well as processing ASSIGN requires Version 11 or later.