# Non-Compliant Behaviour of Automated Vehicles in a Mixed Traffic Environment
###### Abstract  
Legal requirements for minimum distances between vehicles are often not met for short periods of time, especially when changing lanes on multi-lane roads. These situations are typically non-hazardous, as human drivers anticipate surrounding traffic, allowing for shorter headways and improved traffic flow. Automated vehicles (AVs), however, are typically designed to maintain strict headway limits, potentially reducing traffic efficiency. Therefore, legal questions arise as to whether mandatory gap and headway limits for AVs may be violated during periods of non-compliance. While traffic flow simulation is a common method for analyzing AV impacts, previous studies have typically modeled AV behavior using driver models originally designed to replicate human driving. These models are not well suited for representing clearly defined, structured non-compliant maneuvers, as they cannot simulate intentional, rule-deviating strategies. This paper addresses this gap by introducing a concept for AV non-compliant behavior and implementing it as a module within a pre-existing AV driver model. Simulations were conducted on a three-lane highway with an on-ramp under varying traffic volumes and AV penetration rates. The results showed that, with an AV-penetration rate of more than 25%, road capacity at highway entrances could be increased and travel times reduced by over 20%, provided that AVs were allowed to merge with a legal gap of 0.9 s and a minimum non-compliant gap of 0.6 s lasting up to 3 s. This suggests that performance gains are achievable under adjusted legal requirements. In addition, the proposed framework can serve as a foundation for further development of AV driver models aiming at improving traffic efficiency while maintaining regulatory compliance. vehicle headway; automated vehicles; regulatory framework; non-compliant trajectories; motorways and on-ramp 2  
short time periods, especially in dense traffic situations. By applying small decelerations, they restore their desired following headway. This behavior is known as a relaxation phenomenon. Depending on the regulatory framework, this might not be allowed for AVs, which makes some maneuvers very challenging, lane-changing in particular. The UN Regulation 157 was the first relevant global regulation that defined the type-approval process for automated driving systems. Additionally, a proposal for amendments to the UN Regulation, including a regulatory framework for car-following and lane change maneuvers was published in May 2022 [3]. It was suggested that an AV should not perform a lane change if this hinders a lag vehicle in the target lane. In urgent situations, the regulation proposes that AVs should aim not to make an approaching vehicle in the target lane decelerate more than 3 m/s\({}^{2}\). The regulation mainly focused on a framework for developing AVs from an automotive manufacturer perspective. The effects on traffic safety were studied in the paper by [PERSON] et al. [4], but to the best of our knowledge, no detailed analyses have been conducted as to how such regulations influence traffic flow. This is a crucial aspect, as policy makers on a national and international level should also consider potential impacts on traffic flow characteristics when revising and adapting the current regulatory framework for automated driving. For such analyses, traffic flow simulation (TFS) is a suitable tool and has already been applied in previous studies. While TFS was originally developed to model human driver behavior, current researchers try to research and integrate additional features to also allow modeling AVs. On this matter, [PERSON] et al. [5] defined six aspects to consider for modeling automated driving functions in traffic simulation: (1) the role of authorities; (2) user acceptance/preferences; (3) the vehicle system, including the AV driving functions; (4) vehicle perception; (5) vehicle connectivity; and (6) physical/digital infrastructure.