Let's work with an actual example, the expansion of Interstate 10 in Katy, TX. http://www.chron.com/disp/story.mpl/metropolitan/5450155.html http://www.chron.c

Let's work with an actual example, the expansion of Interstate 10 in Katy, TX. http://www.chron.com/disp/story.mpl/metropolitan/5450155.html http://www.chron.com/disp/story.mpl/metropolitan/5450155.htm... Estimated cost: $2.8 billion Traffic: 207,000 per day (http://www.katyfreeway.org/background.html http://www.katyfreeway.org/background.html) Length: 22 miles Cost per mile per daily trip: $614.84 If we're paying it off over 20 years, that's 8.4 cents per mile driven. This doesn't include any necessary maintenance over those 20 years. I doubt the 20-30 cents figure is wrong. The person who was quoted was an elected official who dealt with a lot of transportation issues.