The issue here is that you are prioritizing using "the fast lane in a floating price system" as the most important thing when for a lot of people that will not be the case.
They might rather spend that money on housing, or education or chewing gum or who the hell knows what.
The utility maximizing choice it to let them make their own decision as they know more about their preferences than you do. You making that decision for them destroys utility.
I don't know why the downvotes, you make valid points.
I think what you say is true, but not in the context of this specific scenario. This scenario starts with a public good that is freely available to all.
In the free-for-all, everyone has equal access to the good. The total value of that is somewhat diminished in theory, because the lack of a price system causes overconsumption ... traffic jams.
In the price system, there is a luxury option. In principle, options are good. If you really want to travel fast, you can for a price. In practice though (because income distribution), most of that negotiation does not happen within one person debating if he really wants that fast lane today. There will be some people (wealthy) for whom it is almost always worthwhile and others for whom it is never worthwhile.
What I am arguing is that calling this highest value use is just false.
Choice here does not extend to substitutes. You don't get anything for taking the slow lane.
This is why I'd like to see some less theoretically pure economists tinker with this. It's possible to create a system where what you say is true. This one is impractical, but one example could be a system where fast lane drivers pay slow lane drivers. Ie, negative pricing.
Maybe you earn fast lane credits for taking the slow lane, to be used in lieu of £40. That way all commuters get a taste.
Seems to me that increasing the toll price with increasing levels of road usage would be the best way to ensure that those of lesser means still have access to the express roadway.
Example: Using the express roadway once a month is $10/use. Using it 100 times is 50/use.
This is similar to how California tries to restrict water usage by the wealthy.
They might rather spend that money on housing, or education or chewing gum or who the hell knows what.
The utility maximizing choice it to let them make their own decision as they know more about their preferences than you do. You making that decision for them destroys utility.