So basically what you are saying is... that you still don't get it.
Now we've gone from the false "but we already paid for the roads!" argument to the "it's a foreign company!" argument. Where are these studies that show a toll won't be able to pay off the original cost of construction if gas is $3/gallon? People will continue to use automobilies, regardless of what they are powered by, and thus the demand for use of tolls is independent of the demand for gasoline. The US and the rest of the world have already begun to shift away from conventional gasoline, and that trend is unlikely to stop so long as gasoline prices are high. Unless we go to flying cars and everyone decides they don't want to live on the northside anymore, demand for use of the toll road won't be an issue.
It doesn't matter if it a foreign company or a domestic one, if that company defaults on it's loan, then someone else will have to pick up the tab. Congrats on your "duh!" moment of the day, Dan. It doesn't matter if they are based in Spain or in San Antonio - it all works out the same.
Um... ANY roads will compete for scarce resources, regardless of how they are paid for. Engineers and concrete won't suddenly be in more supply if the government announces they will pay for the roads with some indexed gas tax. The self-perpetuating cycle is a product of your own complaining nature.
On another note, private industry have proved TIME AND TIME AGAIN far more efficient in reducing the costs of... well, anything. Government en ies are the most inefficient organizations at construction because they have absolutely no incentive to reduce costs. A cost overrun of 50% or a timeline slipping by 2 years at a government agency results in no firings, just another check being sent from the state office. The government paying for the roads will increase the general costs of roads much more than a private company entering the market place.
Any road that is currently "free" (nothing none of them are free, you just have to pay per use) SHOULD NOT be turned into a toll road. There is one decent argument you have. Doing that forces consumers who have made previous economic decisions (where to live, for example) into a higher level of expenditure. Smart toll-road planning leaves free lanes and provides toll lanes for those people who value getting where they want to go.
Indexing the gas tax is one way to fund roads... you are still paying for it exactly the same. Whether you pay for it when you get on a toll ramp (which you have an OPTION not to do) or you pay for it with every gallon you put in your tank of gas, you are still paying for it! What are these "far cheaper costs"? Engineers, asphalt and concrete aren't going to get cheaper because you index the gas tax either. The cost is the same. Indexing backers like yourself also like to point out that "we can just index the gas tax, we don't have to raise it..." - well you can't raise MORE money by leaving the tax the SAME! They aren't going to index it downward!
But, as I've repeated, the tolls aren't meant to find a way to pay for the road. They accomplish that, but they also are a means of reducing traffic flow. The equilibrium price of the toll should be where the quan y of use on the toll road leaves a healthy flow of traffic as an alternative to sitting in a parking lot (like 1604 is today). Which leads me to...
Building more free roads has NEVER proven a long term solution. Economics 101, so long as a public good is "free" to use, it will be subject to overcrowding, or in other words, the equilibrium quan y exchanged will be less than the socially optimal quan y exchanged. (This problem remains when ALL roads are tolled at the same rate).
The idea of toll is to provide choice. You are welcome to sit in traffic all day, just like you do now. No one will take that choice away from you. However, if you want to pay just a small fee, you can skip all the traffic.
That small fee discourages use from some buyers, which is precisely how traffic on the toll roads remains managable and presents a value to the potential consumer. If the toll roads are too cheap, that is if the value they provide is greater than the toll, then they will be overcrowded and they've failed. If the toll is too expensive, then the road will be undercrowded and someone has paid to construct a useless road. This cannot take place in an "all-free" road environment.
As for your question "when", just look at any major city that has supplemented free roads with toll roads. Dallas is a great example. No transportation solution is "long term" however, because of population growth. Even New York city's subway system (which I'm sure mass transit is what you are getting at) is subject to overcrowding because the use of it keeps growing. Toll roads are not a permanent solution, but there isn't one. The long term solution is a phased one. You start with toll roads in the outer reaches (which also have the effect of reducing sprawl as the perceived cost of living in the suburbs increases). Then you phase in mass transit solutions in the inner areas of the city, eventually reaching the outer. Again, see Dallas. Dallas' metro is over 3x larger than San Antonio's however.