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Making the most of road traffic data to test operating measures for carpooling reserved lanes

Using data to create HOV lanes

Reserved lanes for carpooling on roads and motorways: how to operate them?

Reserved Lanes for carpooling on road or motorway infrastructures (so called HOV lanes) are on the rise in France! This type of traffic management measure aims to reserve a lane for carpoolers and vehicles with very low CO2 emissions. The objective is simple: to save travel time for carpoolers compared to solo-driver and thus participate in the decarbonization of road mobility.

Their experimentation process, initiated by article 56 of the French TECV law (Energy Transition for Green Growth) consolidated with the French LOM (Mobility Orientation Law) then generalized with the recommendations of the French CCC (Citizen's Convention on the Climate) has created a framework for their launch in several French metropolitan areas. The methodology for feasibility studies of such HOV lanes is also consolidating as well as the technical doctrine for HOV lanes operations tends favor dynamic traffic management operations: the reserved lanes are activated temporarily, and often supporter by dynamic speed limits measures.

However, even if many experimental initiatives are emerging in France, the commissioning of these reserved lanes in a non-experimental operating framework requires roads and motorways operators to deploy advanced algorithms for the automation of such complex traffic management operations.

Combining HOV lanes dynamic activation and dynamic speed limit management

The metropolis of Lyon inaugurated its reserved lane in September 2019. The reserved lane has been deployed on the motorway M6-M7 corridor. The HOV lane is located on the left lane of the motorway section and is marked by a variable message sign displaying a diamond-shaped symbol when activated. It is actived all day during the week and deactivated at weekends. In the continuity of the M6-M7 corridor, the Road Directorate Center East (DIRCE) is studying the possibility of new reserved lanes on the A7 motorway in the south of Lyon.

DIRCE awarded a consortium led by the Cerema (Leading French public institute for traffic and mobility engineering) and Neovya with the feasibility studies for the extension of this reserved lane on its road network. The equipment provided to materialize this reserved lane on the field are variable message sign. Making the most of this equipment in place and to provide a more robust traffic management process able to face various traffic conditions, the need for an advanced algorithm has emerged: a true innovation combining dynamic management of HOV reserved lanes with dynamic speed limit management.

The interest of a digital twin to test the automation of these traffic management measures

The principles of the algorithm are inspired by those of the dynamic speed limit measure elaborated by the Cerema in the years 2010. It is based on a sectioning of the road network. Each section is attributed with a status: “reserved lane activated or deactivated”, with an authorized speed limit of between 50 and 90 km / h. The recommendation generated by the algorithm's decision tree is based on the data streams collected from the traffic sensors on the road network (flow and speed data), enabling to define the actions on each section. Several additional treatments ensure a continuity of service matching with operating requirements: avoidance of excessive speed differentials, inadvertent activations - deactivations over time or on the route of the same motorist, etc.

Due to its advanced level of innovation, the algorithm and its robustness are tested both on real offline data and also in a controlled virtual environment, a real digital twin, reproducing real traffic conditions and enabling the opportunity to lead dynamic tests in several traffic situations.

The implementation of the algorithm in the controlled simulation environment clearly shows its positive impact on traffic conditions using a carefully chosen set of indicators. Comparisons of scenarios reproducing situations without traffic management measure, with static measure and with dynamic measure provide key information to predict operating situations combining the two types of traffic management measures (activated HOV lane and dynamic speed limit). To conclude, the tests carried out in the virtual simulation environment have shown the importance of introducing parameters to avoid the oscillation of state between reserved lane activated and deactivated.

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