Think about what decisions you make when driving not only the control of the car, they are the ones a driverless car cannot make. Is that person wanting to use the crossing. You have right of way but moving slow and a car wants to pull out of the side road you ease of and let them. Parked cars either side leaving enough room for only one vehicle down the centre drivers share the priority, driverless cars would be facing each other not moving. How would it pull out where it's sensors cannot 'see' approaching traffic.
Feel free to come up with a hundred other logical situations they can't handle.
That's before you get to weather conditions.