Whilst contractors and engineers and politicians have many incentives to cut corners when producing public works which will not be consumed at any kind of margin, but "freely", private entities have the incentive to make their infrastructure double strong and of higher quality in order to produce a superior product, while meeting costs precisely at the margin.
That said, my physics professor waxed eloquent on the marvels of science, engineering, and the human mind in a way that would make Ayn Rand gush.
Bridges and buildings are a wondrous thing, and the more I travel and stare at them the more I marvel. Oh, what things man hath wrong out of rock and sand! What a reflection of the mind of the creator in man's creations.