“Shorter toll facilities, including highway spurs and bridges, typically have higher per-mile costs. A March survey by the Pennsylvania Turnpike found 10 facilities with per-mile rates of 27.8 cents or more, including a 6-mile highway in California whose users pay 45.8 cents per mile.”
I paid about $1/mile in Colorado on the E470 toll a few months ago. I was only on the road 1 mile in each direction. Perhaps they charge more for very short uses of the road.
This would have been my guess as top toll fee road. Used it several years ago, going from I25 NE to I40 to bypass the horrible Denver traffic. Seems every couple miles there was another tool booth and another $ toll.
Live in the Colorado Springs area and drive up to the airport (DEN) from time to time, better fares. I avoid I-470, taking I-225 instead. Mileage wise it's about the same, although rush hour traffic can slow your trip. I-470 doesn't have a congestion problem, even in rush hour traffic for obvious reasons ... the tolls are ridiculous.