Taxpayer subsidies for roads etc. vs. public transport

reader Laurie sends this great comment (lifted cactus style):

My sister-in-law ***************************(director of a system in the US). Here's the Q I sent her:

How do taxpayer subsidies for private transportation (roads etc)
compare to subsidies for public?

Here's her answer:
Good question. Local roads and highways get much more than transit; the question is how much more.

It's a hard question to answer because most funds that go toward local streets and roads are not fully accounted for; they are buried in City budgets, whereas public transit funds are fully accounted for and transparent. Also, highway funds are usually allocated to the state and sometimes are used for local freeway maintenance or for local roads or even for some transit. Consequently, it is often hard to even account for all the subsidies that go toward local streets and roads and highways.

However, when you think about all subsidies that go toward local streets and roads, it's not hard to see. Even private funds pay for roads that go places like shopping centers. And municipal bonds that pay for the city hall also pay for the new parking lot and the road leading up to it. Or the water treatment plant and the access roads. Or any other public or private buiding.

It's very rare that municipal bonds pay for transit but it does happen--we recently passed prop 1b which included transit capital funds. But even there, 70% went to streets and 30% went to transit.
Laurie

Update: Identification made more anonymous