It's a scarce good, which loses most of its value if overused.
The standard Econ solution is to set a price that maximizes throughput. At least some toll roads are attempting to hit that price.
In the US, toll roads are required by law to maintain a certain minimum speed. The price is set based on that.
In the US, toll roads are required by law to maintain a certain minimum speed. The price is set based on that.