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Steve Chiotakis: Today, a House committee takes up a $500 billion transportation bill. But a couple of questions remain: How much goes where? And of course, where’s the money coming from? Here’s Marketplace’s Sam Eaton.

Sam Eaton: The transportation bill introduced by Minnesota Democrat James Oberstar would replace the current one, which expires in September. It would also inject badly-needed cash into the Highway Trust Fund. It’s set to run dry in August.

The bill has won praise from environmental groups and transportation officials. It would boost the share of funding for mass transit projects, including $50 billion for high-speed rail. But some supporters of mass transit say the bill still gives highways too much of the cash.

Transportation for America Director James Corless says that doesn’t bode well, especially since cars account for a third of U.S. greenhouse gases.

James Corless: We’ve got nice language in there to suggest we should reduce those, but not a lot of the details about exactly how you’re going to do that from a transportation perspective and how we’re going to pay for it.

Current transportation funding comes from a federal gas tax of about 18 cents a gallon. But with Americans driving less for the second year in a row, revenues have taken a dive. And with little support for raising the gas tax, the question of how to pay for it isn’t going to go away.

I’m Sam Eaton for Marketplace.