Active safety effectiveness assessment by combination of traffic flow simulation and crash-simulation

Advanced Driver Assistance Systems (ADAS) such as autonomous emergency braking systems (AEB) are an increasingly common focus for newly introduced car models. Before such systems can be released to the market, they have to be tested thoroughly to ensure that they work as intended. In general, active safety functions are influenced by a high number of factors, such as traffic flow, sight obstructions, lighting conditions and others. It is very difficult to physically test these factors in a reproducible way. Simulations offer the possibility to consider such a variety of influences even in complex situations. The objective of this study is to define and demonstrate a new approach that allows prospective effectiveness assessment of ADAS systems. The novelty of this method is the combination of the traffic flow simulation software PTV VISSIM with the crash-simulation software PC-Crash. This approach is unique as VISSIM generates distinct and realistic traffic scenarios, instead of relying on in-depth databases as scenario sources. Furthermore, it considers not only two conflicting vehicles, but also the environmental traffic, which potentially plays a major role for the used sensors in terms of sight obstructions and thus visibility of other vehicles. First, a real traffic site is chosen as subject of investigation, limiting the scope of the traffic flow simulation. In this study, an intersection and its connecting roads in the city of Graz (Austria) were chosen, simulating one hour of morning peak traffic in VISSIM. The resulting vehicle trajectories are then analyzed based on safety surrogate measures such as TTC (time to collision) or PET (post encroachment time) by SSAM (Safety Surrogate Assessment Model). Safety surrogate measures correlate with criticality of traffic situations, leading to a certain number of traffic conflicts. In this method, the conflicts are re-simulated in crash-simulation using PC-Crash and the automation platform X-RATE (Extended Effectiveness Rating of Advanced Driver Assistance Systems) for simulation of active safety systems. For these active systems, specifications such as sensor range, sensor opening angle and system reaction time are varied automatically. For demonstration purposes, a simple geometrical sensor model and an autonomous emergency brake system were used which brakes when a specific TTC-threshold is reached. By performing a variation for all detected conflicts, it becomes possible to determine the minimum system specifications required to achieve a specific safety benefit at this traffic site, e.g. avoidance of accidents or mitigation of the consequences in case of collisions. In this study, a parameter variation with subsequent simulation in X-RATE was conducted for a single conflict situation. Results showed which system configurations can avoid the accident, mitigate the consequences or do not provide any safety benefit for the selected conflict. Moreover, it was shown that environmental vehicles that are not directly involved in a conflict can play a crucial role for the visibility of potential collision partners. They can be the deciding factor whether accidents can be avoided or not, even when ideal sensor properties are assumed. In a further step and as an outlook, all the conflicts during the simulation timeframe have to be resimulated in the crashsimulation with parameter variations in order to achieve a more holistic assessment of the system capabilities.