Why the qualification of "in United States"? When it comes to mass transit, and transportation in general, we should be looking to almost anywhere else than the US, because our governments at every level are owned by various corporations and business sectors that profit massively and directly from both car-focused transportation policies and the massive government subsidies, direct and indirect, that they receive through those policies.

In the US, the main places you will find free transit are university campuses. But there are a number of cities who offer varying amounts of free transit, from small buses that run through areas of heavy tourism and shopping, to citywide free buses. Cities in numerous cities worldwide offer free transit for part or all of their users, and quite successfully.

Your assertions in your reply are not based on anything except misconceptions and faulty assumptions. Any given system that relies on fare collection only expects those fares to cover roughly 10% of its budget. Eliminating those fares increases ridership significantly (which is a good thing), and is seen by many as a low-cost but high-impact way to reduce economic inequality.

>Private businesses/delivery ppl could subsidize certain transportation expenses onto the taxpayer.

As for this sentence, I don't know what it means. Businesses already put the expense of employee travel on the employees who have to buy and maintain cars, and the government which builds and maintains roads, etc. And I can't see delivery people ever significantly relying on trains and buses; even if we successfully ban private vehicles in part or all of the city, commercial delivery vehicles would still likely be allowed, and lots of deliveries in urban areas are made by bike and scooter bikes.

Fare free systems have challenges and would certainly take political capital to enact anywhere in the US. But the net benefits can be significant for business, residents, tourists, everyone. Given our climate crisis, governments should probably be paying and otherwise incentivizing everyone possible to take transit rather than private cars. Just saying you have a robust transportation network that's FREE has difficult to measure benefits for attracting both residents and businesses, which in turn grows the tax base to fund just such a system.

https://en.wikipedia.org/wiki/Free_public_transport

https://www.cnbc.com/2020/03/02/free-public-transportation-is-a-reality-in-100-citiesheres-why.html

https://qz.com/2048165/american-cities-are-experimenting-with-free-public-transit

https://www.inverse.com/culture/free-public-transportation-scientific-studies