What's the crux of this concern?
If it's environmental, we can assume cars in the future will be all-electric, powered by nuclear or renewable energy sources.
If it's congestion, firstly we should see a dramatic reduction in the number of accidents. Automated vehicles will make far more efficient use of limited road capacity, and with no need for parked cars to litter urban streets, we will have greater capacity.
More importantly, we can just regulate against congestion. Cap the number of cars in an area at any one time, if you want, or implement dynamic pricing. That will go a long way to eliminating unnecessary journeys during peak times.