  As the development of autonomous vehicles progresses, efficient safety
assurance methods become increasingly necessary. Safety assurance methods such
as monitoring and scenario-based testing call for formalisation of driving
scenarios. In this paper, we develop a temporal-logic formalisation of an
important class of critical scenarios in the ISO standard 34502. We use signal
temporal logic (STL) as a logical formalism. Our formalisation has two main
features: 1) modular composition of logical formulas for systematic and
comprehensive formalisation (following the compositional methodology of ISO
34502); 2) use of the RSS distance for defining danger. We find our
formalisation comes with few parameters to tune thanks to the RSS distance. We
experimentally evaluated our formalisation; using its results, we discuss the
validity of our formalisation and its stability with respect to the choice of
some parameter values.
