I don’t see how saying that “public will is an impediment to solving traffic congestion” indicates contempt for the public. It seems like a straight-forward factual statement, and not a particularly controversial one.

After we acknowledge that “public will” is an impediment, we can then probe whether the problem is really so bad after all, what “public will” really means, whether it is self-contradictory, how strongly entrenched those interests/ideas are, whether there are ways of reframing the conversation to significantly sway public perception and action, and so on.

It might turn out that everyone loves griping about traffic congestion but isn’t really too bothered. Or that “public will” is just reflexive opposition to misunderstood alternatives conditioned by decades of deliberate propaganda. Or that “public will” is very weakly held and malleable if an alternative proposal does a charismatic marketing blitz. Or that the disparate powerful interest groups involved are in direct opposition and political progress working towards compromise is at a total impasse and impossible. Or ...

Op said that "public will is an impediment to progress". That is much more arrogant statement than the one you claim to defend: "public will is an impediment to solving traffic congestion"

The context made it abundantly clear that this meant “... impediment to progress [with respect to traffic congestion]”.

Not just that the public is generically “anti-progress”.