I agree it is difficult to quantify the costs, but I wanted to get an idea. A quick analysis shows that while a system like BART may operate at a loss of about

I agree it is difficult to quantify the costs, but I wanted to get an idea. A quick analysis shows that while a system like BART may operate at a loss of about one dollar per trip, that is not far off from the costs of operating our car and road network. Based on average fuel economy, and road expenses the state of California subsidies driving at a rate of about 6.2 cents per mile. I didn't find any hard sources, but a few references that the average commute may be about 12 miles. That would make the average subsidy for a commute to be about $0.75. - BART looses about a dollar per trip: (https://www.citylab.com/transportation/2015/06/how-much-money-us-transit-systems-lose-per-trip-in-1-chart/395189/ https://www.citylab.com/transportation/2015/06/how-much-mone...) - California gas tax covers 22.7% of road costs: (https://taxfoundation.org/gasoline-taxes-and-tolls-pay-only-third-state-local-road-spending/ https://taxfoundation.org/gasoline-taxes-and-tolls-pay-only-...) - Average fuel economy is 23.6 miles / gallon in the USA: (https://www.washingtonpost.com/news/wonk/wp/2013/12/13/cars-in-the-u-s-are-more-fuel-efficient-than-ever-heres-how-it-happened/?utm_term=.11eedf94c1db https://www.washingtonpost.com/news/wonk/wp/2013/12/13/cars-...) - The gas tax is 48.6 cents per gallon. Math: - Total road expense per gallon of gas sold: 0.486/0.227 = $2.14 - Subsidy: 2.14-0.486 = $1.65 - Per mile $1.65/26.6 = $0.062