Motion
planning in dynamic environment is crucial to the automated driving safety. In
extremely emergency scenarios with unavoidable collisions, especially those with
complex impact patterns, the potential crash risk should be well considered in
motion planning. This paper proposes a motion planning algorithm for unavoidable
collisions, which directly embeds a generalized crash severity index model to
vehicle-to-vehicle collisions of multiple impact patterns. Firstly, the
clothoid curve is used to sample the vehicle trajectory before collision, and a
two-degree-of-freedom model is adopted to predict the vehicle poses
corresponding to each sample path. Then, the crash severity index model is to
estimate the potential crash severity of all sample paths. To improve the
inferring time efficiency, a neural network is constructed and deployed to
approximate the nonlinear severity model. Finally, the crash-severity-optimal
trajectory is tracked through model predictive control method. Results show
that by combining the braking and steering interventions for better crash
severity reduction, the proposed strategy can achieve better mitigation effects
than commonly-used collision-avoidance strategies. The deployment of real car
experiment and sensitivity analysis demonstrate that the planning algorithm can
guarantee real-time and reliably safe performances.