I guess Christian Wolmar has never driven a car in an urban environment. Pedestrians dart out into the road. Even if the driver isn't too busy on their smartphone, or listening to the radio, or talking to the passengers, it still takes 3/4 of a second at best to go from recognizing a danger to pressing the brake pedal. At 25mph that's almost 30 feet. An autonomous system would be able to respond much faster.
We've spent 100 years getting the roads to work for human drivers, and that is leveraging centuries of knowledge of horse drawn vehicle traffic. Just like we have signage for humans, roads will need signage for autonomous vehicles.