I can assure you, there are way more humans causing massive traffic problems than a few meme vids on YT, e.g. every fender bender on a crowded road can tie up traffic for hours. Countries without self driving cars are not without traffic jams after all.

As mentioned below, in a world of self driving cars, there's no reason to even own a car, so the total number of cars will be way, way less... Most cars - which take enormous resources and cause enormous pollution to build when you take into account all of the aspects of mining the resources, producing the parts, assembling the car, etc, and in the end disposing of the car - spend most of their time sitting idle. An efficient system of on demand self driving cars could handle all of the trips we take now in a fraction of the number of cars, eliminating the waste associated with little-used cars. It's trivial for an AI to figure out how to combine multiple passengers going to and from the same places at the same time into the same car, thus handling high volume times like rush hour and preventing the need for the fleet volume to be scaled just to the high volume times. Fewer cars then has downstream impact on other resource usage like parking, parts production and maintenance, etc.

Ultimately the argument is more based on safety than economics but the economics are definitely positive as well.