It's likely correct that mass transit is directly subsidized at a greater percentage than any specific aspect of private car ownership. However, there are significant indirect subsidies due to the centrality of private cars that not only dwarf transit subsidies, but simultaneously make transit less economical.
A simple example is minimum requirements for parking. Almost every home and business is paying more for additional space that cars take up. This means less people in catchment areas for different types of transit.
A simple example is minimum requirements for parking. Almost every home and business is paying more for additional space that cars take up. This means less people in catchment areas for different types of transit.