aveo ai?

i was wondering (as i do quite frequently) why we dont have cars that drive themselves yet, well i know they do but they are unidirectional as far as i know. like street worthy cars that know the rules of the road and can act instantly to sudden obstacles. its seems to me a computer would be a better driver than the average earth citizen. would anyone be able to give me a rough estimate on how much processing speed would actually be needed to
observe, react and calculate the act of daily driving?

i know it seems a little od to ask but this is probably the only place i know of to look for information like that