OK, let's look at several examples. On a typical highway most drivers use only a portion in literally thousand of different start and endpoints, so I'll give some common ones. Since they moved the route of TTC-35 on the DFW end (in response to feedback from local govt's and the public in the hearing process, so much for the anti-TTC lies about not responding to public comment) most users will get on the TTC around Venus, coming from the Dallas area on US 67, which is what I'll use for the northern end. Many from Ft. Worth will enter around Mansfield from US 287, about 6 miles north, so add $1 to the cost for them. Others would get on at I-20/360, which is almost 11 miles further north, so for them add another $1.65 (that assumes that the future mainlanes of 360 south of I-20 will be built as toll lanes, north of there it is already freeway.)
On the TTC, Venus-the outlet shops at Hillsboro is 25 miles, so $3.75 ($6.40 from I-20.) Double if a round-trip, though many may choose to use the free roads in one direction if they are traveling at an off-peak time.
Venus-Waco exit (TX 30) is 87 miles, so $8.55 (to $11.20.)
Venus-Temple/Killeen/Ft. Hood exit (US 190) is 132 miles, so $19.80 (to $22.45.)
Venus-Georgetown exit is 158 miles, $23.70 ($26.35.)
Venus-Round Rock exit is 174 miles, $26.10 ($28.75.)
Venus-US 290/US183 interchange (where the 290 mainlanes that are already built begin, 6 miles from the state capitol complex) is 189 miles, $28.35 ($31.00.)
So at the $.15 per mile rate, going from DFW to the capitol is about $30 one-way. That may seem high to the average Joe, but there are plenty of lobbyists, local officials, businessmen, etc. who would gladly expense account it, a lot cheaper for the business/gov't entity then an airline ticket. Especially considering that with a speed limit of 85 mph it would be about a 3 hour or so trip, competitive door to door with air travel. Cheaper than a hotel room for those with morning meetings.
For those headede to San Marcos, the tourist areas around New Braunfels, and San Antonio that just want to loop around Austin, it is 218 miles, $32.70 ($35.35.)
All the way from DFW to I-10 east of San Antonio (where the TTC will end for the first 10-15 years) is about 250 miles, $37.50 (to $40.15.)
Plus all the users from Waco, Temple, north Austin, Austin, south Austin, New Braunfels, and various areas of San Antonio and all the combinations of trips they can make. Most of the trips under $40 (really under $30.) When you think of all the business travel that will expense account it, and the speed factor making it competitive and cheaper than airfare and avoiding some hotel stays, Cintra's projected use at even $.15 per mile may indeed be realistic.
Plus, you don't have to take your shoes off and leave behind all your liquids when entering the highway.