Reducing traffic seems like one of the most effective uses of self-driving technology. Driverless buses and trains allowing increased frequency would reduce traffic, and avoiding toxic human-driver behavior such as tailgating, aggressive merging and so forth. All things being equal driverless technology could plausibly be much better for traffic. Air-pollution can can already be solved by electric cars, so that doesn’t seem like a good objection. You’re also not addressing the safety issues pointed out as being most impressive.