SIDRA ASSIGN · Route choice in practice
Can SIDRA help you analyse route choice effects in traffic modelling?
SIDRA ASSIGN combines traffic assignment with the lane-based SIDRA Network model, so route choice effects can be assessed alongside detailed intersection and network performance.
In a real-world case (with vehicles driving on the left-hand side of the road), queues on the west approach of a roundabout were blocking an upstream freeway interchange. A metered roundabout was proposed to control the east approach which had a large right turning volume reducing the capacity of the west approach.
Roundabout metering (holding east approach briefly to create gaps for the west approach) was applied to the east approach to reduce queues and delays on the west approach.
What the SIDRA ASSIGN model showed
SIDRA ASSIGN's equilibrium traffic assignment modelling showed that a significant proportion of traffic would divert to an alternative route as a result of the metering.
Route | Before | After | Change |
1Route through the metered East approach | 907 veh/h | 413 veh/h | ↓ 494 |
2Alternative route using South approach | 43 veh/h | 537 veh/h | ↑ 494 |
This large amount of route diversion proved to be a significant factor in assessing the proposed scheme.
Why this changes the assessment
A diversion of this size is not a footnote to the scheme. It is part of what the scheme does:
- Some of the opposing (circulating) flows to the west approach that originally entered the roundabout at the metered east approach would divert and now enter the roundabout at the unmetered south approach. This impacted the effectiveness of the roundabout metering scheme.
- The reduced capacity of the metered east approach of the roundabout would result in significant lane blockage and capacity reduction that could negatively impact westbound traffic. The availability of an alternative route provided the westbound traffic another viable route option which reduced the negative impacts of the roundabout metering scheme to the westbound traffic.
- The alternative route now carries more than ten times its previous volume. Its intersections, its capacity and its suitability for that traffic all need assessing.
An analysis that models this network with fixed traffic volumes and without consideration of route choice behaviour would not be able to assess these impacts.
This may not be a typical case but many traffic management schemes such as changes to traffic signal phasing, lane reallocation, turn bans, introducing or changing one-way roads and access restrictions are likely to have significant effects like this.
About SIDRA ASSIGN
We developed SIDRA ASSIGN as a micro-analytical traffic assignment model integrated with the lane-based, multimodal SIDRA Network model. Its level of detail makes it particularly suitable for analysing small-to-medium-sized critical network areas.
Lane level, not link level | Route travel times come from detailed analysis of intersection delays in the SIDRA Network model, capturing lane blockage, the resulting constraint on downstream arrival flows, and signal timing effects that link-based macroscopic tools have difficulty representing. |
Five assignment methods | Stochastic User Equilibrium (the default), User Equilibrium, Fixed Route Assignment, Incremental and All-or-Nothing. Fixed Routes can be used together with the other methods, which is useful for buses, trams, trucks and bicycles. |
Multimodal | Assignment by movement class: light vehicles, heavy vehicles, buses, bicycles, large trucks and light rail/trams, plus user-defined classes. |
Best fit | Corridor studies, paired intersections, interchange assessments and area-wide traffic management schemes: the critical areas where route choice interacts with intersection performance. |
Learn more about SIDRA ASSIGN →
Want to learn how to use it?
Our next SIDRA ASSIGN online training session runs on Wednesday 9 September 2026. It is a hands-on 3.5-hour workshop led by Dr Rahmi Akçelik, author of SIDRA INTERSECTION, and Dr Ian Espada. It covers traffic assignment fundamentals, the ASSIGN data and methods, convergence metrics and O-D volumes, worked through four examples and a practice exercise.
SIDRA ASSIGN – Online Training TE-171
Wednesday, 9 September 2026 | 10:00 am – 1:30 pm AEST
Live online (Livestorm) · Certificate of Completion · 3.5 hrs CPD/PDH
$594.00 AUD inc. GST
A working knowledge of SIDRA INTERSECTION is recommended. New to SIDRA? Start with INTRODUCTION TO SIDRA first. Software and a temporary FLOATING Licence are sent to attendees before the session, and two monitors are required, so it is worth registering early. Full program, presenters and setup requirements are on the course page →