In the US, toll roads are required by law to maintain a certain minimum speed. The price is set based on that.
What law?
I suppose "regulation" would be more accurate, and it only applies to HOV lanes that receive funding from a specific source:
https://ops.fhwa.dot.gov/freewaymgmt/hovguidance/chapter4.ht...
This covers pretty much all of the lanes that people complain about so I'll stand by what I said.
That's interesting, but also a significantly narrower category than all toll roads.
The standard Econ solution is to set a price that maximizes throughput. At least some toll roads are attempting to hit that price.