All of those taxes are already per vehicle. The license plate tax is per vehicle. The tax paid on a gallon of gas is per vehicle. Tolls are per vehicle. There is already an embedded penalty for low occupancy because the costs are spread across fewer people. Fighting congestion is already a major cost: time. Who are you trying to decongest the roads for? How will you avoid creating a situation where only the wealthy are allowed to drive, and now all you've accomplished is making their driving experience more pleasant?