Also, consider that with enough driverless cars, the congestion at intersections should be reduced (many lights will no longer be needed, especially during low-traffic times like night.) The danger at congested stops would be equal to now, and it is nearly impossible to drive away from danger in a multi-lane column of stopped traffic.

So the answer is, you don't. The sort of fine-grained, always on surveillance necessary for driverless cars to work would be applied outside the cars as well as inside. Pedestrians are dangerous, with or without a gun, and as soon as you walk outside and attempt to interact with the urban environment without the safety of a self-driving car, someone would be alerted. Your identity will be confirmed, you will be tracked and every self-driving car for miles will know about it.

So in your scenario, the proper authorities have been called before you were even aware of his presence, simply because there was a human near traffic.