The George Bush Turnpike takes its own tolls. I don't think Dallas has any problem getting loans to fund new highways until they can take tolls to pay it off.
Let's do a little research and see where all those tolls go. I'll have to bet they don't all get used on roads. Besides....they take road fees out of each and every auto registration we pay for.
They were built by the same agency, the North Texas Tollway Authority. Tolls from the NDT helped pay for construction of the GWB, and tolls from both will help pay for all the extensions to each and probably the toll road to be built southwest from downtown Ft. Worth. Once the 121 mainlane construction is finally approved for tollroad construction, they'll fund that, too. I'm not certain that 100% of the NTTA receipts are reinvested in roads, but am willing to bet that that is the case. As for the state gas tax, IIRC 30% is diverted to education, with the rest going for road projects. However that now barely covers the maintenance costs, because while project costs rise with inflation, the gas tax stays a constant amount, and the percentage of road construction costs paid for by federal dollars has decreased.
Here's their website:
http://www.ntta.org/pub/servlet/pubfrontpage
I'm not affiliated with them, but did look into toll roads a few years ago when I was adamently against toll roads(hated the Pennsy and Jersey turnpikes.) Now that I've read up and seen the math, I'm all for most of them, it is the only way to speed up road construction without raising taxes. The state can only issue so many bonds, but they can issue more if there is future toll income to pledge. And if a private company builds and finances them, then they(and their investors) take on the risk.