Traffic Simulation System

Definition and Technical Concepts

A traffic simulation system refers to dynamic analysis technology that utilises digital computer models to replicate complex traffic phenomena. Its primary role is to replicate and forecast the operational conditions of existing or future traffic networks by modelling temporal and spatial variations in traffic flow, thereby delivering analysis, diagnostics, and optimisation solutions for complex traffic scenarios. Compared with conventional traffic analysis methods, simulation technology effectively captures the stochastic nature of traffic flow, enabling cost-effective and safe preliminary assessments of traffic management proposals in a controlled and repeatable environment, thereby mitigating the costs and risks associated with on-site trials.

Hierarchical Architecture: From Macro to Micro

Traffic simulation systems are typically categorised into three tiers—macroscopic, mesoscopic, and microscopic—based on the level of detail applied in modelling the traffic network.

Macroscopic traffic simulation relies on aggregate models covering traffic volume, speed, and density to capture the overall vehicle flow across a road network without detailing individual driver behaviours like lane changing, making it ideal for macro-scale analyses such as transport planning and network structural evaluations.

Mesoscopic traffic simulation treats multi-vehicle platoons as the fundamental modelling unit to describe vehicle ingress and egress across road links and junctions, approximating manoeuvres like lane changing in a simplified manner, which suits regional traffic demand forecasting and medium-scale scheme appraisals.

Microscopic traffic simulation uses individual vehicles as the core modelling unit, precisely capturing real-world driving behaviours such as car-following, overtaking, and lane changes. It is extensively applied for detailed assessments across urban junctions, public transport networks, and slip road merges, representing the most widely utilised and technically demanding tier of simulation. Popular microscopic simulation platforms include PTV Vissim from Germany, Aimsun from Spain, open-source SUMO, and TESS NG from China, among others.

Typical Application Scenarios

Traffic simulation systems play a pivotal role in engineering practice. For scheme evaluation and optimisation, they serve to appraise road upgrading proposals or traffic diversion plans during roadworks, proactively pinpointing bottlenecks through predictive modelling. For traffic light control optimisation, multiple simulation iterations can be conducted on signal timing plans to achieve the most efficient timing strategy. For major events and emergency traffic management, they simulate the impact of special events across the road network, aiding in the design of robust traffic dispersal and diversion plans.

Domestically, proprietary microscopic simulation software has been successfully commercialised for smart highway management and the deployment of digital twin systems. Several cities have also developed integrated local traffic models, synchronising simulation engines with real-time traffic control data to continuously calibrate models and accurately reflect live road conditions.

Technical Limitations

The accuracy and reliability of traffic simulation systems depend heavily on precise parameter calibration, the quality of input data, and how accurately the algorithms replicate real-world driving habits. Inaccurate calibration or reliance on unverified default parameters can cause simulation outputs to deviate significantly from actual road conditions, leading to "simulation distortion". Consequently, rigorous model calibration prior to simulation runs and thorough validation afterwards are essential to ensure the results deliver dependable, actionable insights.