How do you define "safe driving" in terms a machine can understand?

WHEN people learn to drive, they subconsciously absorb what are colloquially known as the "rules of the road". When is it safe to go around a double-parked vehicle? When pulling out of a side street into traffic, what is the smallest gap you should try to fit into, and how much should oncoming traffic be expected to brake? The rules, of course, are no such thing: they are ambiguous, open to interpretation and rely heavily on common sense. The rules can be broken in an emergency, or to avoid an a...