This project sounded unique, so I found it interesting and read the presentation. Regarding legal authority, it says "Tolls may be imposed on existing toll-free highways, bridges & tunnels so long as variable pricing is used to manage demand. No formal federal approval process other than NEPA." It also mentions the three slots for conversion to toll roads, but since they plan to charge lower rates at night, the project qualifies under the demand management provision needing only environmental approval.
It doesn't give toll point locations, but it says they will be between urban areas. This would make travel across cities toll-free. It also says "Commuters travel first two gantries free." I thought about whether that refers only to some kind of qualified commuter, but I concluded it probably includes everyone. Since there are so few toll points, each one will be quite expensive. It would be unfair to enter the Interstate and take the next exit a mile later and get charged for 50 miles of road just because you happened to cross a toll point. Similarly, you could cross two toll points driving as little as 40 miles and be charged for about 100. They could remove that inequity by charging only if you go through three points. There's still some potential inequity, but the proportionality is reduced, so that it's in the range of overcharging encountered on other barrier-type toll roads. However, it then says "Auto Annual Pass could eliminate commuter/non-commuter distinction." This suggests that "commuter" means "commuter" and that severe overcharging for a short drive will be possible.
The presentation also mentions intersections with other Interstates, suggesting the toll points might just happen to end up within concurrencies if they do charge for passing a single toll point. It also mentions "near state borders" which has an obvious meaning.
Other interesting points: "Toll rates generate sufficient revenues to finance the I-81 Corridor Improvement Plan; but is not a revenue maximization strategy."
"Establish toll rates and other programs that discourage diversion." Low rates and possibly lower speed limits and disruptive traffic controls on parallel routes.