Imperfect but much better than existing implementations. Really, though, the goal ought to be not only to reduce congestion, but to fairly distribute the net gain of utility among those affected.
A marginal $20 has very little utility to rich people, but 15 minutes saved in traffic has large utility. Congestion pricing results in large utility gains to the rich.
A marginal $20 has tangible utility to poor people, and 15 minutes spent finding alternative transport also has tangible utility. Congestion pricing results in large utility losses to the poor.
KBB values are an imperfect proxy for individual monetary utility but could definitely be used to more fairly distribute the utility gains from congestion pricing.
The main problem with that scheme is that its imprecision falls exactly where I think we need the highest precision: The ultra-rich. If they're just a passenger in their driver's black SUV (maybe $100k KBB tops), they're not paying anywhere close to a commensurate share of their income on congestion fees. The upper middle class BMW driver, on the other hand, gets screwed (relatively speaking).
The congestion charge should reach each person using that infrastructure in a way that fairly impacts their available individual utility. The impracticality of achieving this goal is why, in my opinion, congestion charges are bad policy.
Avoiding a policy that makes life better for nearly everyone because it doesn't make life bad enough for the top 0.0001% is so absurd that I honestly can't believe it's the source of your real opposition.
Given the extreme wealth disparity in this country, there will be virtually no policies at all that achieve your platonic policy-making ideal. Should we just have no laws at all?
If you really care to deal with the extreme high-end, there are other mechanisms that are easier to do at small n, such as having a superlinear vehicle registration tax.
A marginal $20 has very little utility to rich people, but 15 minutes saved in traffic has large utility. Congestion pricing results in large utility gains to the rich.
A marginal $20 has tangible utility to poor people, and 15 minutes spent finding alternative transport also has tangible utility. Congestion pricing results in large utility losses to the poor.
KBB values are an imperfect proxy for individual monetary utility but could definitely be used to more fairly distribute the utility gains from congestion pricing.