This. Especially in cities, where car usage is a classic example of the tragedy of the commons. I personally would love to see the entirety of public transportation in major cities paid for by those who want to drive. Muni, BART, CalTrain, NYC Subway, etc. should all be funded via a tax on those who prefer to drive in a region where public transportation exists.
See, this is where I have to disagree - I think people who insist on driving their own cars should fund those who take public transport.
The government is trying to encourage public transportation - that puts less stress on roads and infrastructure, it causes less pollution and damage to the environment, and means roads are less congested.
Also, public transport is one of those funny things that actually gets better the more people use it.
Fares will go down, and you'd get more frequent services.