United States Department of Transportation
i
Highway Safety and Traffic Flow Analysis of Mixed traffic with Connected and Non-Connected Vehicles
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2022-09-01
[PDF-1.50 MB]
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Edition:Final report (Aug. 2020–Dec. 2021)
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Abstract:Safety is the number one issue in the deployment of any vehicle technology. This leads to two interconnected challenges. First, how to ensure safety without having a significant negative impact in traffic flow. Second, how will varying penetrations of autonomous vehicles (AVs) impact safety and efficiency in mixed traffic. To address these issues, we start by proposing a risk metric that takes into account the severity of a collision that would happen under a worst-case scenario and the time the vehicle is exposed to such a collision. With this definition, we propose an autonomous lane changing procedure in which the vehicle behaves as if it was simultaneously on both lanes. This ensure that the vehicle never puts itself in a collision prone situation. Given the conservative nature of this approach, which can negatively impact traffic flow, we include the possibility of the AV accepting risks in its gap acceptance decision process. We extend this approach to a scenario with connected and autonomous vehicles (CAV), which can cooperate to generate lane change gaps through communications. In this case, a CAV in the destination lane also behaves as if it was simultaneously on two lanes, thus generating the gap for the incoming vehicle. We perform extensive micro simulations using the commercial software VISSIM with varying percentages of AVs and CAVs, different vehicle inputs, and several accepted risk values. Results indicate that, while AVs need to accept small risks in order to achieve the same traffic flow efficiency as humans, CAVs can improve both safety and efficiency without having to accept any risks. Our results also indicate that AVs and CAVs still behave safely in mixed fleets, but they do not bring significant improvements in traffic flow.
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