Automated online recognition of unexpected conditions is an indispensable component of autonomous vehicles to ensure safety even in unknown and uncertain situations. In this paper we propose a runtime monitoring technique rooted in the attention maps computed by explainable artificial intelligence techniques. Our approach, implemented in a tool called ThirdEye, turns attention maps into confidence scores that are used to discriminate safe from unsafe driving behaviours. The intuition is that uncommon attention maps are associated with unexpected runtime conditions.

In our empirical study, we evaluated the effectiveness of different configurations of ThirdEye at predicting simulation-based injected failures induced by both unknown conditions (adverse weather and lighting) and unsafe/uncertain conditions created with mutation testing. Results show that, overall, ThirdEye can predict 98% misbehaviours, up to three seconds in advance, outperforming a state-of-the-art failure predictor for autonomous vehicles.