system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do suspension bridge decks curve upward?

On pictures of Suspension bridges, there is a noticeable curve on the road deck, is there a particular reason as to why it happens?
gpt
If it were flat, and any weight was added to it, it would bend downwards. Nothing can be perfectly stiff. By starting with an upwards bend, once it bends down it will either be flat or still bend upwards. 

Also, at any location of the bridge, the neighboring locations are curved away below/behind it. This helps distribute the load from where it’s located to neighboring parts of the bridge. This is the basic idea of an *arch*, which has been used with everything from basic stone construction to concrete dams and suspension bridges.