In most other parts of the world, roads and highways are not subsidized to the extent they are in the US. Gas taxes are much higher, and cover most if not all of the cost of road construction and maintenance. With the billions of dollars of subsidies for roads in the US, it is impossible for any other form of transit to compete.

NYC MTA does not make any profit and has no apparent way of making any profit, and therefore its "stock", if it existed, would be completely worthless.

However, many cities in the US contract with private companies to operate their public transit systems. These companies have stock that can be bought on the stock exchange like any other company.