18th February, 2025
Lampros Yfantis
Scientific Researcher, Aimsun
Can Tradable Mobility Credits be effective, as “digital tolls“, for interurban mobility management? How could DRT services be utilized in an interurban context to further enhance network efficiency? This article outlines how Aimsun, in collaboration with the @LICIT-ECO7 laboratory of Université Gustave Eiffel, deployed simulation to assess interurban innovations for the Mediterranean Highway pilot of the DIT4TraM Project.
The removal of tolls on parts of Spain’s AP-7 highway in 2021 led to a significant surge in traffic demand. This increase has impacted negatively the highway’s Level of Service (LoS), particularly during peak periods and in cases of unforeseen incidents/accidents. Recognizing this challenge, the Mediterranean Higway pilot in DIT4TraM aimed to:
These objectives highlight the necessity of analyzing innovation deployments towards balancing demand across the interurban highway network, managing efficiently incidents, increase the Level of Service and, subsequently, reduce emissions. The focus area of the pilot is the AP-7 and N-II corridors in the periphery of the city of Girona, which produces and attracts high interuban demand flows.
The original AP-7 Aimsun Next model and the refined Girona scope
The first innovation investigated in the virtual Mediterranean Highway pilot is a quantity-based TCS for interurban traffic management. This system incentivizes drivers to use alternative routes by rationing highway access through a virtual credit system. Key features included:
This system aims to optimize traffic distribution and reduce congestion while maintaining equitable infrastructure access.
Complementing the TCS, the pilot further introduced a flexible digital P&R service, offering first-/last-mile options for trips from and to the city of Girona, leveraging app-based pre-booking systems for parking and ride-sharing van services. Designed to alleviate urban congestion, the P&R schemes has been assumed to provide:
The aim of the P&R service is to induce a mode shift that will bundle originally single private car trips into a more sustainable first- and last-mile door-to-door van-sharing service with parking options in the periphery (and the center) of the city, and thus, reduce traffic demand volumes on the highway network (and the city).
The pilot utilized an agent-based simulation framework – detailed in a previous Aimsun article – which is powered by the Aimsun Next Microscopic Traffic Simulator. This dual-layer approach integrates:
The simulation-based scheme analysis framework for the Mediterranean Highway pilot
The AP-7 feasibility study has been based on two main scenarios – i.e., Scenario 1: TCS intervention as a standalone, and Scenario 2: Combined TCS and P&R strategies – while considering a planned roadwork scenario on AP-7 (lane closures). For each scenario, different experiments have been conducted given a pre-defined set of parameter and scenario variable specifications inlcuding VoT and logit parameters for route choices, credit allocation rates and initial credit prices, equilibrium (price and model convergence) thresholds as well as demand penetration and service design assumptions for the digital P&R service (e.g., fleet size and capacities, parking locations and schedules).
Simulations revealed that, for Scenario 1, a credit allocation rate tuning between 70%-80% is the most beneficial on both the AP-7 and system level. The equilibrated credit price is 0.9 Euros, which means that even a few dozen cents are enough to have a positive impact. For a 70% credit allocation range, AP-7 has seen a significant reduction of travel times (↓ up to 22%), delays (↓ up to 85%) and densities (↓ up to 57%) and an increase in speed (↑ up to 22%). However, on the system level, for the same allocation rate, while speed and density are marginally higer and lower respecitvely, higher travel times and delays are observed. The adverse effect on the system level is attributed to the increasing trafic volume redistributed to N-II causing higher “pressure” on a more limited capacity national road and its intersections. Any credit allocation rate below 60% results to spillback effects from N-II to AP-7 on interesections, reducing the original benefits stemming from the traffic volume reduction on AP-7.
Results from Scenario 2 further enhanced the original hypothesis for higer improvements on both the AP-7 and system level, while it’s clear that for higher P&R demand penetration rates the benefit rate is inreasing substantially on AP-7 around Girona, but not significantly on the network level, where it remains relatively stable. The geographical positioning of parking/depot hubs for the flexible P&R service is critical. It needs to be ensured that the increasing traffic demand produced and attracted locally by the new P&R serice will be facilitated efficiently by the road network capacities around the hub locations.
Due to the unlimited DRT fleet size assumption (a vehicle is generated if needed given the demand level) and given that parking occupancies and service operations have not been modelled in detail, the added benefit ranges contain a bias degree which limits the reliability of the Scenario 2 results. Further sensitivity analysis and modelling detail is required for the P&R scenario.
The Mediterranean Highway Pilot underscores the potential of robust simulation-based planning for innovative demand management scheme assessments. The Mediterranean Highway Pilot showcased preliminary results on the efficacy of integrating advanced traffic management schemes and new first- and last-mile services on interurban mobility networks. Key takeaways include:
Building on these successes, the pilot team envisions further development, including, expanding the integration of flexible P&R within TMC systems, conducting extensive sensitivity analyses and modelling in more detail the flexible P&R operations and the resulted emissions.
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Aimsun Next 24
Aimsun (2024). Aimsun Next 24 User’s Manual, Aimsun Next Version 24.0.0, Barcelona, Spain. Accessed on: April. 16, 2024. [Online].
Available: https://docs.aimsun.com/next/24.0.0/
Aimsun Next 24
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address = {Barcelona, Spain},
year = {2024. [Online]},
month = {Accessed on: Month, Day, Year},
url = {https://docs.aimsun.com/next/24.0.0},
}
Aimsun Next 24
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UR – [In software]. Available:
https://docs.aimsun.com/next/24.0.0/
