It doesn't cross a river. It's not a train trestle. Its main purpose is to carry automobile traffic across a deep arroyo, the Arroyo Seco, from Pasadena to Los Angeles and vice versa. I believe its secondary purpose is to be beautiful.
Yet I never tire of the Colorado Street Bridge. I don't get tired of photographing it, crossing it or gazing at it. In fact when it's in my view I can't take my eyes off it. It's one of the prettiest bridges I've ever seen.
Some have said that form must follow function, but to follow it exclusively is to be deprived of opportunity for beauty. I'm a fan of the odd superfluous detail, myself.