  Classical approaches and procedures for testing of automated vehicles of SAE
levels 1 and 2 were based on defined scenarios with specific maneuvers,
depending on the function under test. For automated driving systems (ADS) of
SAE level 3+, the scenario space is infinite and calling for virtual testing
and verification. However, even in simulation, the generation of
safety-relevant scenarios for ADS is expensive and time-consuming. This leads
to a demand for stochastic and realistic traffic simulation. Therefore,
microscopic traffic flow simulation models (TFSM) are becoming a crucial part
of scenario-based testing of ADS. In this paper, a co-simulation between the
multi-body simulation software IPG CarMaker and the microscopic traffic flow
simulation software (TFSS) PTV Vissim is used. Although the TFSS could provide
realistic and stochastic behavior of the traffic participants, safety-critical
scenarios (SCS) occur rarely. In order to avoid this, a novel Stress Testing
Method (STM) is introduced. With this method, traffic participants are
manipulated via external driver DLL interface from PTV Vissim in the vicinity
of the vehicle under test in order to provoke defined critical maneuvers
derived from statistical accident data on highways in Austria. These external
driver models imitate human driving errors, resulting in an increase of
safety-critical scenarios. As a result, the presented STM method contributes to
an increase of safety-relevant scenarios for verification, testing and
assessment of ADS.
