Simulating traffic flows with connected vehicles

Roberto Ponticelli explains how the UK connected and intelligent traffic environment will help simulate how traffic will flow when vehicles can communicate with infrastructure and each other.

Traffic simulation has traditionally been used by local authorities and road network managers to analyse city transport systems and assess proposed changes.

On the verge of new mobility options and technologies, these tools must evolve into systems simulators, able to cope with more than just simplified flow models of traffic or vehicle-level interactions. With the development of Advanced Driver Assistance Systems (ADAS) features as well as autonomous features now more commonly present on new car models such as Autonomous Emergency Braking (AEB), engineers must re-think how to effectively model the future vehicle traffic.


The modern vehicle is part of a wider network, with the ability to talk to surrounding cars and infrastructure for improved safety and efficiency

One particular technology that will affect how traffic is modelled today is the Vehicle-to-All (V2X) communications, whereby a vehicle is no longer a single agent or entity interacting with just those other entities surrounding it. With V2X communications, vehicles are connected to a complex arrangement of entities: other cars far beyond the line-of-sight, traffic lights, pedestrians, cyclists, etc.

The difference between normal car traffic and connected car traffic can be illustrated by modelling the behaviour in a game of pool. In a normal game of pool, each of the 16 balls behaves as normally expected, in function of the force, direction and contact position by which a ball is hit. Traditional modelling can cope with the variables in normal car traffic, but this significantly changes with connected car traffic. If you take the same pool table but add in the variable of awareness, where each ball interacts with each ball around it, it becomes incredibly complex to simulate what will happen. This is because each ball is “aware” of what the neighbouring balls are doing, so react not only to the contact events but also to what the other balls are doing at the same time. For example, all balls numbered below eight will avoid contact with balls numbered over eight.

A frequently depicted scenario of connected vehicles is where hundreds of vehicles approach a complex intersection and are able to communicate their location, speed and intentions. It could be possible to remove traffic lights in such scenarios, given the level of coordination that all the vehicles crossing the intersection can achieve, as a consequence of not only reacting to the car in front of them but to all the cars around the intersection.

For this type of scenario, a bespoke simulation platform needs to be developed that supports the communications in a traffic environment (between vehicles and with other entities – V2X), and the reactions to those communications (within each vehicle and each other V2X-enabled entity). In addition, simulation must support normal interactions between vehicles and other entities in their environment.

As part of the UK Connected and Intelligent Traffic Environment (UK CITE) project, HORIBA MIRA is developing a traffic simulation system to support the study of the different use cases of Connected Vehicles (CV) technologies and meet the challenges they present.

This includes the integration of the state-of-the-art traffic simulation tool PTV Vissim to other renowned software tools in the quest of accurately modelling and simulating V2X communications in traffic environments. HORIBA MIRA is also including the option for human drivers to interact with the simulation through a driving simulation rig.

Among the possibilities this setup offers is the augmentation of the well-accepted traffic modelling capabilities of Vissim to include V2X communications and specific behaviours of the vehicles equipped with V2X applications.. This enables engineers to study and assess how the traffic changes and how the human driver reacts to the newly available information enabled by the V2X communications.

As we continue to hurtle towards greater connectivity, we must ensure that the new technologies being developed for connected driving are safe and secure. These simulation tools will be essential as already complex systems become ever more intricate, before they are deployed on our roads.

Simulating traffic flows with connected vehicles

Simulation of a hypothetical road network model, showing traffic of normal vehicles (in red) and connected vehicles (in blue). To the right, the lines represent V2X communications taking place between those connected vehicles in range.

Roberto Ponticelli is chief engineer for intelligent mobility at automotive engineering services provider HORIBA MIRA