Not quite the same thing, but to get the average occupancy per car, they apparently just ask people. https://www.energy.gov/eere/vehicles/articles/fotw-1040-ju

Not quite the same thing, but to get the average occupancy per car, they apparently just ask people. https://www.energy.gov/eere/vehicles/articles/fotw-1040-july-30-2018-average-vehicle-occupancy-remains-unchanged-2009-2017 https://www.energy.gov/eere/vehicles/articles/fotw-1040-july... https://nhts.ornl.gov/ https://nhts.ornl.gov/