One (probably not so simple) way could be to build up a shared database of input-decision-outcome records, so when a car is faced with some unknown object on a

One (probably not so simple) way could be to build up a shared database of input-decision-outcome records, so when a car is faced with some unknown object on a particular street, or its own risk assessment is high (e.g. heuristics- "I am planning to decelerate quickly"), it could search for similar input patterns (e.g. color, shape, gait) or similar decision plans in the database, and bias the car's own decision accordingly to avoid an undesirable outcome. Then that decision would get posted to the database as well, linked to its parent. Previous outcomes in the database could be assessed by humans in some kind of legal framework to help the cars determine undesirable vs desirable outcomes.