Something struck me as odd when reading through this post. You mentioned how toll roads often use previous highways, and you explicitly cite Highway 290. I am from Houston and have traveled on this road many times, and 290 is never used as a toll road, it goes downtown from the West where it ends at the inner 610 loop, never once costing a penny.
As far as I know, Houston has 2 toll roads, the Beltway and the Hardy Toll Road. The
Beltway is just a giant circle around Houston, and the Hardy Toll Road simply runs from the North parallel to I-45 and 59 towards downtown. The reason for me pointing out the physical relation of these roads is to illustrate that these roads are not required to get anywhere in Houston. That's the point of toll roads, to alleviate traffic, but not to serve as necessary routes of transportation. The toll is an effective way of charging those who use the roads the most.
Because these roads are not used by everyone, why should everybody have to pay taxes for these roads? As we learned, the legislature is required to spell out where all state funds go, and if one were properly motivated enough, you could look up where all of our tax money goes.
In this issue, it's very important to note what our two alternatives are to not having tolls. We can either A) increase a general tax, or B) apply a gasoline tax. While I'm sure many Texans may be upset over toll fees, I'm almost positive that the last thing a Texan wants to see is gas prices go up one more red cent. Also, both of these solutions blanket citizens that may have nothing to do with the cost or usage of these roads.
One last thing to note is that toll road contracts are given out to private investors, not a public sector company. Because of this, there's a profit to be had. A great read as to why private companies win out these bids is illustrated here.
The heart of this discussion can be found here.