Transit is more expensive externalities included
The 2015 cost of Transit is roughly 71 cents per passenger mile averaged - https://www.transit.dot.gov/sites/fta.dot.gov/files/docs/Transit%20Profiles%202015%20-%20Top%2050%20Agencies%20with%20Summary.pdf
Buses are 1.08 dollars per passenger mile, Heavy Rail is 49 cents per passenger mile, commuter rail is 50 cents per passenger mile, hybrid rail is 93 cents per passenger mile, bus Rapid Transit is 80 cents per passenger mile, commuter buses are 62 cents per passenger mile, and light rail is 77 cents per passenger mile.
Amtrak in 2019 spent 3.5 billion dollars to move 6.4 billion passenger miles. Or roughly 54 cents per passenger mile. Amtrak is not technically transit, but it's similar.
https://www.enotrans.org/article/amtrak-concedes-perpetual-1-billion-year-operating-losses/
https://www.statista.com/statistics/185800/us-passenger-miles-by-intercity-or-amtrak-since-1990/
A 2006 study puts the cost of automobile externalities at roughly 8.8 cents per vehicle mile. Considering externalities for cars and not transit is not really fair because transit has externalities too, but there no studies or data calculating it. Study Here: https://media.rff.org/archive/files/sharepoint/WorkImages/Download/RFF-DP-06-26.pdf
I use this to adjust for inflation https://www.usinflationcalculator.com/
So Roughly 13 cents per vehicle mile in externalities.
If we assume that roads are 100 percent subsidized (not really true, some per capita vehicle expenditures go to roads, but they are funded in a weird sort of way), they cost roughly 621 dollars for every 10,000 vehicle miles, which is roughly 0.06 cents per vehicle mile - https://www.urban.org/policy-centers/cross-center-initiatives/state-and-local-finance-initiative/state-and-local-backgrounders/highway-and-road-expenditures
The Average American Spends 4,800 dollars on vehicle related expenditures.
https://www.statista.com/statistics/748911/us-average-per-capita-vehicle-spending-by-category/
The Average American travels 14,263 vehicle miles
https://www.thezebra.com/resources/driving/average-miles-driven-per-year/
This is roughly 34 cents per vehicle mile.
Per vehicle mile driving is roughly 53 cents per vehicle mile, externalities included and assuming a 100 percent road subsidy and assuming no externalities for transit.
The Average American car has an occupancy 1.5 persons per vehicle
https://css.umich.edu/publications/factsheets/mobility/personal-transportation-factsheet
The unsubsidized cost of driving is roughly 35 cents per passenger mile.
By comparison Transit in Japan is almost universally profitable from fares. The Tokyo Monorail, for example, charges 500 yen for its highest fare over the full distance of train, which is roughly 3.85 over a distance of 11.1 miles, which is roughly 35 cents per passenger mile, and it does this while making a profit. The Monorail has lower fares available as well.
https://www.lightrailnow.org/myths/m_monorail005.htm
https://www.tokyo-monorail.co.jp/english/guidance/train_info.html
https://en.wikipedia.org/wiki/Tokyo_Monorail
By comparison New York City, where Transit is heavily utilized, spends 50 cents per passenger mile on the subway, while charging 35 cents per passenger mile. By comparison the London Underground costs 43 cents per passenger mile to run.
https://twitter.com/chittimarco/status/1431333517250764809
It's not simply a problem of ridership, even in New York where ridership is high, the operating costs are inflated relative to other parts of the world.
New York to Paterson Jitney fares cost roughly 6 dollars over 22 miles of distance, which is roughly 27 cents per passenger mile, while making a profit. https://www.jerseyjitneys.info/?page_id=11
Bus operating costs are largely inflated by inefficient union work rules and other inefficiencies
"Existing evidence suggests that transit contracting can provide services at costs 10 to 50 percent below public agency cost levels"
https://onlinepubs.trb.org/Onlinepubs/trr/1987/1108/1108-001.pdf
The NYC subway and other NY trains have inflated operating costs due to practices like having conductors. NY also spends 4 - 5 times as much on track maintenance as Paris due to Union work rules.
https://pedestrianobservations.com/2015/07/26/why-labor-efficiency-is-important/
https://www.vox.com/policy-and-politics/2017/7/11/15949284/new-york-subway-crisis
Caltrain maintains not only conductors, but the position of "assistant" conductors
https://caltrain-hsr.blogspot.com/2020/05/the-cost-of-conductors.html
Amtrak (While not technically transit), uses roughly 45 employees per Long Distance train and 5 per short distance train, neither of which is a particularly great
https://www.amtrak.com/content/dam/projects/dotcom/english/public/documents/corporate/position-papers/white-paper-amtrak-long-distance-financial-performance.pdf
According to Wendell Cox, both transit and Amtrak have seen a 50% or more decline in per worker productivity compared to private sector predecessors.
http://www.publicpurpose.com/ut-tr&cprod-1997.htm
I would emphasize this is not an argument against transit itself, but that the economics of American transit is so piss poor that driving is more cost effective externalities included and assuming a 100 percent road subsidy. American Transit has a cost effectiveness problem. Transit in America is largely an exercise in value destruction.