system
Given the following post, respond as if you're commenting on Reddit:
human
Why aren't all bridges basically the same shape?

Some are arches, trapezoids, suspension, etc. I can see that for different loads you would have to have more/less superstructure, but all the railway bridges I'm passing on this train from NYC to DC are all supporting basically the same thing (me, and the train I'm in), and the lengths of the spans are not that far off. And yet, I've noticed many different types! It can't be an aesthetic decision, so what gives? Thanks, Scientists!
gpt
Civil engineer here. It depends on many factors which include what kind of vehicles will be traveling over it, what kind of forces it will have to sustain, what the geography is, what the climate is, what is it spanning across, what materials are going to be used, the length of the span, etc.