Due to the presence of the roadâ\euro™s curvature and sensorsâ\euro™ limited field of view, as-built highway curves designed based on traditional human-driven vehiclesâ\euro™ characteristics pose a challenge to the adaptive cruise control (ACC) system and its shared control. However, very few efforts in the literature were expended on exploring the adaptability of the ACC system-dedicated vehicle (V-ACC) from the perspective of vehicle-road geometry interaction. Therefore, the objectives of this study are threefold: (i) to investigate the implications of existing horizontal curves on V-ACC dynamic and kinematic characteristics; (ii) to unravel the impact mechanism of curve geometric features; and (iii) to evaluate the ACC systemâ\euro™s adaptability from different aspects and extract the critical curve geometric features. To this end, a virtual co-simulation platform was established and validated by the OpenACC database. A series of tests featuring circular curve radius (RC), desired speed (Vde), and desired clearance were created, and V-ACC characteristics were output. The results show that: (i) a smaller RC causes V-ACC characteristics toward the margins of safety, comfort, and speed consistency, but neither sideslip nor rollover occurs, and speed consistency is good; (ii) the driver and passengers (if any) feel comfortable at Vde = 40, 80-100 km/h following the leading car, but they may feel â\euro˜moderately uncomfortableâ\euro™ at Vde = 50-70 km/h when RC decreases toward its lower limit; and (iii) asymmetrical maneuvers and discomfort would exist before and after the circular curve. These findings could help road administrators regulate V-ACCâ\euro™s behaviors and improve its road-oriented operation design domain.

Most existing road infrastructures were constructed before the emergence of automated vehicles (AV) without considering their operational needs. Whether and how AV could safely adapt to as-built highway geometry remain inconclusive, and a plausible concern is a challenge from vertical alignments. To fill this gap, this study uses virtual simulation to investigate the available sight distance (ASD) for AV on vertical alignments subject to the current highway geometric design specification, and its implications for speed limits. According to the scenario generation framework, several scenarios featuring vertical geometric elements and the light detection and ranging (LiDAR) sensor were created and tested. Moreover, the maximum speed for adequate ASD is calculated to determine the AV speed limit, considering safe sight distance and speed consistency requirements. The results indicate that crest curves are not disadvantaged in ASD compared with either the sag curves or tangent grades. Only equipped with multi-channel LiDAR and advanced perception algorithms enabling a lower detection threshold, would Level 4 AV be compatible with the as-built vertical alignment with a design speed (Vd) of 100 km/h. However, Level 3 AV can only adapt to the vertical profile with Vd = 60 km/h. The findings of this study should be of interest to the road-oriented operational design domain and support road administrators in regulating AV safe speeds.