https://www.technologyreview.com/s/415041/new-measure-of-hum...
I don't think we know enough about how the human brain works yet to give a precise value, but just on caloric arguments I would say that the mean processing power of the brain is not significantly above what we have now in general purpose computing devices.
It's memory + control driven with visual feedback, not much more. You don't have to solve anything if you already sorta know the solution, and can adjust it for the goal.
You can find other figures, but many are in the petaflop range, well above what could be realistically installed in a vehicle.