Congestion pricing should really be called decongestion pricing. Its purpose is to provide an alternative to sitting in congestion for people and businesses willing to pay the fair price for the scarce road space required. The toll isn't a tax, it's a price for driving in an uncongested lane. So if your toll lane is still congested, you're not doing (de)congestion pricing, and your results say nothing about whether it's a good idea.
In Crosscut, former Washington State Secretary of Transportation Douglas MacDonald lays out the issue today as it applies to Seattle area freeways. There, likely toll lanes are already High Occupancy Vehicle (HOV) lanes permitting cars with two or more people. Everyone knows that if the goal is free flow, this minimum has to go up to three whenever congestion requires it.
When carpool lanes were first established there was a vigorous “now or later” debate about the right limit for the carpool privilege: two-to-a-car, or three-to-a-car? Pragmatism won. Except for three-to-a-car from the start on the Evergreen Point Bridge, carpool lanes were introduced with the two-to-a-car rule.
Everyone involved at the time believed that later the rule would have to be, and could be, changed to three-to-a-car. Everyone was entirely up-front about this expectation. The trigger would be the growth of traffic in the carpool lanes to the point where access would have to be cut back so that they would still work.
Didn't happen. Good luck today with that ticking time bomb for a political revolt. The moment of truth is at hand, at least for some carpool lane segments. But no one today seriously talks about outright banishing the two-to-a-car carpoolers to thin out jammed carpool lanes.
I defer to Doug's knowledge of Washington State politics, but I do resist the apathy-inducing hyperbole of the phrase "no one talks seriously." Is "everyone" sure that changing carpool lanes to 3+ would trigger a political revolt if it also caused people to start getting to work on time? Especially if the state also put some effort into casual carpool facilities at the same time? Especially if transit riders (in buses in the same lanes) began getting to work on time too? I wonder. I can see it would be controversial. I can see it would take some time. But can no one "seriously" discuss it?